JPH1079548A - Semiconductor laser control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor laser control device which is easily integrated, lessened in power consumption, and enhanced in drive speed by a method, wherein a single chip is made to comprise an integrated circuit composed of a specific pulse width modulation-intensity modulation signal generating section, an error-amplifying section, and a current drive section, and the current drive section is provided in an optical-electrical negative feedback loop. SOLUTION: A pulse width modulation-intensity modulation signal generating section 22 generates light emission command signals, an error amplification section 23 forms an optical-electrical negative feedback loop 3, together with a photodetector 2 to control the current of a semiconductor laser 1 so as to make the detected signals of the photodetector 2 equal to light emission command signals. Moreover, a current drive section 24 outputs a drive current as a forward current to the semiconductor laser 1, corresponding to the light emission command signals generated by the sum of or the difference between the control current of the optical-electrical negative feedback loop 3 and the operating current of the drive section 24. An integrated circuit 20 contained in a single chip is composed of the pulse width modulation-intensity modulation signal generating section 11, the error amplification section 23, and the current drive section 24, and the current drive section 24 is provided inside the optical- electrical negative feedback loop 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a laser printer,
The present invention relates to a semiconductor laser control device for driving and controlling a semiconductor laser used as a light source in a digital copying machine, an optical disk device, an optical communication device, and the like.

[0002]

2. Description of the Related Art Semiconductor lasers are extremely small and can be directly modulated at a high speed by a drive current. Therefore, semiconductor lasers have recently been widely used as light sources for laser printers and the like.

However, the relationship between the drive current and the light output of the semiconductor laser changes remarkably depending on the temperature, and this poses a problem when the light intensity of the semiconductor laser is set to a desired value. In order to solve this problem and take advantage of the semiconductor laser, various APCs (Automatic Power C) have been conventionally used.
ontrol) circuits have been proposed.

The APC circuit is roughly divided into the following three methods. The optical output of the semiconductor laser is monitored by the light receiving element,
An optical / electrical negative feedback loop that constantly controls the forward current of the semiconductor laser so that a signal proportional to the light receiving current proportional to the optical output of the semiconductor laser generated in the light receiving element is equal to the light emission level command signal. To control the optical output of the semiconductor laser to a desired value. During the power setting period, the light output of the semiconductor laser is monitored by the light receiving element, and the signal proportional to the light receiving current (proportional to the light output of the semiconductor laser) generated in the light receiving element is equal to the light emission level command signal. The forward current of the semiconductor laser is controlled as described above, and the optical output of the semiconductor laser is controlled to a desired value by holding the forward value of the semiconductor laser set during the power setting period outside the power setting period. In addition, outside the power setting period, information is loaded on the optical output of the semiconductor laser by modulating the forward current of the semiconductor laser set during the power setting period based on the information. By measuring the temperature of the semiconductor laser and controlling the forward current of the semiconductor laser by the measured temperature signal, or controlling the temperature of the semiconductor laser to be constant, the optical output of the semiconductor laser can be controlled to a desired value. Method to control to value.

In order to set the optical output of the semiconductor laser to a desired value, the following method is desirable. However, the control speed is limited by the operating speed of the light receiving element and the operating speed of the amplification element forming the optical / electrical negative feedback loop. For example, when the crossover frequency in the open loop of the optical / electrical negative feedback loop is considered as a standard of the control speed, and when this crossover frequency is f ₀ , the step response characteristic of the optical output of the semiconductor laser is P _out = P ₀ {1-exp (−2πf ₀ t)} P _out ; light output of the semiconductor laser P ₀ ; set light intensity t of the semiconductor laser t; time

In many applications of semiconductor lasers, the total light amount (integral value of light output ∫P) from immediately after changing the light output of the semiconductor laser until a set time τ ₀ elapses.
_out · dt) is required to have a predetermined value, and ΔP _out · dt = P ₀ · τ ₀ ｛1− (1 / 2πf ₀ τ ₀ )
[1−exp (−2πf ₀ τ ₀ )]｝.

If τ ₀ = 50 ns and the allowable range of error is 0.4%, f ₀ > 800 MHz must be satisfied, which is extremely difficult.

[0008] In addition, the method described above is frequently used because the above-mentioned problem does not occur in the method and the semiconductor laser can be modulated at a high speed. However, according to this method, the light output of the semiconductor laser is not always controlled, so that the light amount of the semiconductor laser fluctuates easily due to disturbance or the like. As the disturbance, for example,
The semiconductor laser has a droop characteristic, and the amount of light of the semiconductor laser easily causes an error of about several percent due to the droop characteristic. As an attempt to suppress the droop characteristic of a semiconductor laser, a method of compensating the thermal time constant of the semiconductor laser with the frequency characteristic of the semiconductor laser drive current has been proposed. However, the thermal time constant of the semiconductor laser is different for each semiconductor laser. There is a problem that there is an individual variation, and that it varies depending on the surrounding environment of the semiconductor laser.

An improved system in consideration of such a point has been proposed in, for example, Japanese Patent Application Laid-Open No. 2-205086. According to the publication, as shown in FIG. 15, the light output of the semiconductor laser 1 is monitored by the light receiving element 2 and the output of the semiconductor laser 1 is constantly set so that the output and the light emission level command signal (DATA) become equal. The optical / electrical negative feedback loop 3 includes an optical / electrical negative feedback loop 3 for controlling a forward current, and a current driver 4 for converting a light emission level command signal (DATA) into a forward current of the semiconductor laser 1. Control current and current driver 4
Discloses a method of controlling the optical output of the semiconductor laser 1 by a current of the sum (or difference) of the drive currents generated by the above. In the illustrated example, the optical and electrical negative feedback loop 3 is constituted by the semiconductor laser 1 and the light receiving element 2 and I _DA1 becomes the constant current source 5 and the inverting amplifier 6, the output of the inverting amplifier 6, the resistance R _e semiconductor The driving transistor 7 connected in series to the laser 1 is driven and controlled. The current driver 4 is a constant current source 8 of I _DA2.
It consists of.

According to this, when the optical output corresponding to the current for directly driving the semiconductor laser 1 by the current driver 4 is P _S , the step response characteristic of the optical output of the semiconductor laser 1 is P _out = P ₀ + (P _S −P ₀ ) ｛1−exp (−2πf ₀ t)
)｝. If P _s ≒ P ₀ , the optical output of the semiconductor laser instantaneously becomes equal to P ₀ , so the value of f ₀ may be smaller than that in the case where only the optical / electrical negative feedback loop 3 is used. FIG. 16A shows how the optical output changes when only the optical / electrical negative feedback loop 3 is used, whereas FIG. 16B shows the case where a constant current I _DA2 is added by the current driver 4. 3 shows how the light output changes. Realistically, f ₀ = 40 MH
It suffices that the frequency is about z, and a crossover frequency of this level can be easily realized.

Next, taking a laser printer as an example, a description will be given of the history of the one-dot multi-value conversion technique. Laser printers were initially developed as non-impact printers to replace line printers.However, laser printers were considered for application as image printers because of their high speed and high resolution, and various recording methods based on the dither method were practically used. Has been In addition, with the rapid progress of semiconductor technology in recent years, the amount of information that can be processed has rapidly increased, and in a laser printer, a one-dot multi-valued technology has been put into practical use. is there. However, the current multi-level level has an output level equivalent to 8 bits in a high-end device, but is suppressed to a value of at most a low-end device. This is partly due to the large amount of information, but mainly due to the large and expensive circuit size of the semiconductor laser control modulation unit that realizes one-dot multilevel output.

At present, as a semiconductor laser control modulation system for performing one-dot multi-level output, there are A.I. Light intensity modulation method B. Pulse width modulation method A pulse width intensity mixed modulation scheme has been proposed.

A. Light intensity modulation method (PM = Power Modu
lation) A method of recording by changing the light output itself. Since halftone recording is realized by using the intermediate exposure area, stabilization of the printing process is an important requirement, and the requirements for the printing process become strict. However, the control modulation of the semiconductor laser becomes easy.

B. Pulse width modulation method (PWM = Pulse
Width Modulation Although the light output level is binary, the light emission time (that is, the pulse width) is changed for recording, so that the use of the intermediate exposure area is less than the PM method, and By combining adjacent dots, the intermediate exposure area can be further reduced (requirements for printing process stability are reduced). However, when the pulse width is set to 8 bits and adjacent dot combination is realized, the configuration of the semiconductor laser control modulator becomes complicated.

C. Pulse width intensity mixed modulation method (PWM +
PM method) The PM method has a severe requirement for stabilizing the printing process, and the PWM method has a problem that the semiconductor laser control modulator is complicated. Therefore, the PM method is a method combining the PM method and the PWM method. For example, see JP-A-6-3
No. 47852 discloses this.

This modulation method is basically a binary recording method, and is based on a PWM method which is stable to a printing process, and complements a transition portion between pulses with a PM method. In the case of realizing the same number of gradations, the required number of pulse widths and the number of power values are reduced by combining these modulation schemes when compared with a single modulation scheme. In addition to being stable to the printing process, it is suitable for integration, and can be reduced in size and cost.

In order to realize such a modulation system, the semiconductor laser control device basically includes a pulse width generation unit and a data modulation unit 11 which input image data and a pixel clock as shown in FIG. The pulse width generation unit and the data modulation unit 11 are provided with a semiconductor laser control unit and a semiconductor laser drive unit 12 having a circuit configuration as illustrated in FIG.
Is configured to output a light emission level command signal DATA corresponding to. That is, the PWM method is used as the basis by the pulse width generation unit and the data modulation unit 11 according to the input image data, and the transition part is complemented by the PM method. FIG. 1 shows a basic conceptual diagram of an optical output waveform of the semiconductor laser.
FIG. FIG. 18 schematically shows an optical output waveform of a semiconductor laser in the case of outputting a total of 18 gradations of three values of pulse width and six values of power.

Since this modulation system is basically a PWM system as shown in the figure, it is necessary for the intensity modulation unit using the intermediate exposure area to output with a minimum pulse width. In order to obtain such an optical output, for example, assuming that the pulse width is PWM as shown in FIG. 19, PWM _OUT and PWM _OUT + P
M _OUT (PM _OUT has a minimum pulse width) or two pulses of PWM _OUT and PM _OUT (PM _OUT has a minimum pulse width) may be generated. By setting all the bits in the pulse of the PWM _OUT pulse to the H level and turning on / off each bit in the pulse of the PM _OUT pulse in accordance with the data, the waveform of the optical output shown in FIGS. 18 and 19 can be obtained. In FIG.
The upper row shows the right mode with right alignment, and the lower row shows the left mode with left alignment.

In order to more specifically realize such a pulse width intensity mixed modulation method in one dot, a pulse width generation unit is simply configured by using an IC using a C-MOS device, and a bipolar transistor is used. For example, Japanese Patent Application Laid-Open No. 6-347852 has proposed a proposal for facilitating the design of an optical / electrical negative feedback loop by using an integrated circuit.

[0020]

However, according to the method disclosed in Japanese Patent Application Laid-Open No. 6-347852, a current addition method for reducing the amount of control by an optical / electrical negative feedback loop and a pulse addition method within one dot are also disclosed. In order to realize the pulse width intensity mixed modulation method with a higher integration degree so as to achieve smaller size and power saving, there is still room for improvement in functioning at higher speed and higher accuracy. is there. In particular, a current driver that controls both the current flowing through the semiconductor laser,
Regarding an error amplifier (for example, the current driver 4 and the inverting amplifier 6 shown in FIG. 15) which constitute a part of the optical / electrical negative feedback loop, they are separately configured and required. This is one of the reasons that it is difficult to achieve further integration, for example, the number of elements is large and the power consumption is large.

Accordingly, the present invention provides a peripheral configuration which facilitates integration by devising a configuration in the vicinity of an error amplifying unit and a current driving unit, and which makes the most of the features associated with such devising. With the goal.

[0022]

According to the first aspect of the present invention,
Based on the input data, a pulse width modulation / intensity modulation signal generation unit that generates a light emission command signal that simultaneously performs pulse width modulation and intensity modulation on the input data, a semiconductor laser, and an optical output of the semiconductor laser. A light receiving signal proportional to the light output of the semiconductor laser obtained from the light receiving element by forming an optical / electrical negative feedback loop together with the light receiving element to be monitored, and a light emission command signal given from the pulse width modulation / intensity modulation signal generation unit; And an error amplifying unit that controls the forward current of the semiconductor laser so that the currents are equal to each other, and is generated so as to control the driving of the semiconductor laser by the sum or difference current of the control current of the optical / electrical negative feedback loop. A current flowing as a forward current to the semiconductor laser according to a light emission command signal given from the pulse width modulation / intensity modulation signal generator. A pulse width modulation / intensity modulation signal generator, an error amplifier, and a current driver are formed by a one-chip integrated circuit, and the current driver is provided with the optical / electrical negative feedback loop. It is provided within.

Therefore, since the current driver is also integrated with the error amplifier and incorporated in the optical / electrical negative feedback loop, the configuration of this portion is small, and further integration can be easily achieved. In particular, since one large current driving part can be used, it is convenient for reducing power consumption and large-scale integration is facilitated. Furthermore, since it is sufficient to drive a small current, high-speed driving is also possible.

According to a second aspect of the present invention, in the semiconductor laser control device of the first aspect, an external element for setting a current value of the pulse width modulation / intensity modulation signal generation section is provided. Therefore, since the current generated from the pulse width modulation / intensity modulation signal generation unit is a DC monitor current of the light receiving element, it is necessary to set the current not to be affected by the temperature change inside the integrated circuit. Is adjusted, the monitor current can be stabilized so that a desired optical output can be obtained in accordance with the characteristics of the semiconductor laser and the light receiving element. Also,
It is also possible to support a wide range of monitor current.

According to a third aspect of the present invention, in the semiconductor laser control device according to the first aspect, an external element for setting a control speed of the optical / electrical negative feedback loop is provided. Therefore,
The degree of freedom in designing the control system is increased, and the control speed can be freely set to a desired value.

According to a fourth aspect of the present invention, in the semiconductor laser control device according to the first aspect, the current driver is a high-speed voltage shifter in the error amplifier, and includes a differential circuit for changing the amount of voltage shift. And is provided in the optical / electrical negative feedback loop. Therefore, further high-speed operation can be easily achieved by the voltage drive by the high-speed voltage shift unit, and the potential can be easily set.

According to a fifth aspect of the present invention, in the semiconductor laser control device of the first aspect, the pulse width modulation / intensity modulation signal generating section outputs a plurality of first light emission command signals and a second light emission command signal. The D / A conversion circuit is shared.
Therefore, in configuring the semiconductor laser control device according to the first aspect, the number of required elements is reduced, and further lower power consumption and integration are facilitated.

According to a sixth aspect of the present invention, there is provided the semiconductor laser control device according to the first aspect, further comprising an offset setting section having an external element for setting an offset current for setting the optical output of the semiconductor laser to a desired minimum value. I have. In order to control the optical output of the semiconductor laser in real time in the optical / electrical negative feedback loop, the optical output of the semiconductor laser cannot be made completely zero. It is necessary to set an offset current as follows, but by using an external element, a desired offset current can be easily set by the offset setting unit.

According to a seventh aspect of the present invention, in the semiconductor laser control device according to the first aspect, the maximum current of the pulse width modulation / intensity modulation signal generation section and the offset current that minimizes the optical output of the semiconductor laser are set. An interlock setting unit having an external element that is set in interlock is provided. Therefore, since the setting of the offset current is performed in conjunction with the setting of the maximum current of the pulse width modulation / intensity modulation signal generation unit, the offset current is automatically set so that the offset current is constant without changing the value of the external element. can do.

According to an eighth aspect of the present invention, in the semiconductor laser control device of the first aspect, an offset setting section having an external element for setting an offset current for setting the optical output of the semiconductor laser to a desired minimum value; An interlock setting unit having an external element for setting the maximum current of the width modulation / intensity modulation signal generation unit and the offset current in an interlocking manner is provided. Therefore, the offset current can be automatically set so as to be constant without changing the value of the external element, and the desired characteristics can be freely adjusted by using the offset setting unit. Can also be provided.

According to a ninth aspect of the present invention, there is provided the semiconductor laser control device according to the first aspect, further comprising a start-up section for permitting the operation to start when the power supply voltage reaches a predetermined potential when the power is turned on. Therefore, if initialization, setting operation for the current driver, and the like are performed before the power supply voltage reaches the predetermined potential when the power is turned on, the optical output of the semiconductor laser may not be a desired value. The start of the operation is permitted after the power supply voltage reaches the predetermined potential by the control of the above, so that the accuracy of the initialization of the integrated circuit can be improved, and the semiconductor laser can be protected at the time of rising.

According to a tenth aspect of the present invention, in the semiconductor laser control device according to the first aspect, the pulse width modulation / intensity modulation signal generating section for flowing the absolute current determined by the light receiving element is provided for the reference current. There is a base current compensator for compensating the base current by the number of switch transistors passing through the base current of the reference current. Therefore, by adding to the reference current by the number of switch transistors passing through the base current of the reference current,
It is possible to suppress the occurrence of an error current and a change in characteristics due to the base current, and to improve the accuracy of the current of the light emission command signal generation unit.

According to an eleventh aspect of the present invention, in the semiconductor laser control device according to the first aspect, an external element for setting a current value of the pulse width modulation / intensity modulation signal generation section is provided, and is determined by the light receiving element. The pulse width modulation / intensity modulation signal generating section for flowing the absolute current has a base current compensating section for compensating the base current by the number of switch transistors passing through the base current of the reference current with respect to the reference current. . Therefore, by adjusting the external elements, the monitor current can be stabilized so that a desired optical output can be obtained in accordance with the characteristics of the semiconductor laser and the light receiving element, and it is possible to cope with a wide range of monitor current. In addition to this, the generation of an error current and a change in characteristics due to the base current can be suppressed, and the current of the pulse width modulation / intensity modulation signal generation unit can be increased in accuracy.

According to a twelfth aspect of the present invention, in the semiconductor laser control device of the first aspect, there are a plurality of pulse width modulation / intensity modulation signal generators. Therefore, it is possible to cope with a wide range of monitor current, and it is possible to cope with a difference in specifications of the semiconductor laser and the light receiving element.

According to a thirteenth aspect of the present invention, in the semiconductor laser control device according to the first aspect, an input terminal of an external control voltage for varying the maximum current of the pulse width modulation / intensity modulation signal generator is provided. Therefore, by dynamically varying the maximum current of the pulse width modulation / intensity modulation signal generation unit by the external control voltage, shading correction during operation and fine adjustment of the light amount can be performed.

According to a fourteenth aspect of the present invention, in the semiconductor laser control device according to the thirteenth aspect, a start-up section for allowing operation to start when a light emission command current corresponding to the light emission command signal reaches a predetermined current when the power is turned on. Have.
Therefore, as in the case of the ninth aspect, it is possible to increase the accuracy of the initialization of the integrated circuit, and to protect the semiconductor laser at the time of rising.

According to a fifteenth aspect of the present invention, in the semiconductor laser control device according to the thirteenth aspect, an additional current setting section for setting a drive current corresponding to a light emission command signal and a maximum of a pulse width modulation / intensity modulation signal generation section. An interlocking unit that interlocks the current with the maximum current set by the addition current setting unit. Therefore, when dynamically shading correction is performed in the invention according to claim 13, the maximum current by the addition current setting unit is also linked, so that the optical output waveform can be made closer to an ideal square wave.

According to a sixteenth aspect of the present invention, in the semiconductor laser control device according to the thirteenth aspect, a start-up unit for allowing the operation to start when a light emission command current corresponding to the light emission command signal reaches a predetermined current when the power is turned on. An addition current setting unit that sets a drive current corresponding to the light emission command signal, and an interlocking unit that interlocks the maximum current by the pulse width modulation / intensity modulation signal generation unit with the maximum current by the addition current setting unit. I have. Therefore, when dynamically shading correction is performed in the invention according to claim 14, the maximum current by the addition current setting unit is also linked, so that the optical output waveform can be made closer to an ideal square wave.

According to a seventeenth aspect of the present invention, in the semiconductor laser control device according to the thirteenth aspect, a first start-up section for allowing operation to start when a power supply voltage reaches a predetermined potential at the time of power-on, A second start-up unit that allows the operation to start when the light emission command current corresponding to the light emission command signal reaches a predetermined current. Therefore, in the invention of the thirteenth aspect, similarly to the inventions of the ninth and fourteenth aspects, the accuracy of the initialization of the integrated circuit can be improved, and the semiconductor laser can be protected at the time of rising.

[0040]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. The semiconductor laser control device of the present invention is applied, for example, as a control device for controlling the optical output of a semiconductor laser used for optical writing in a laser printer or the like. Here, even in the present embodiment, basically, the pulse width intensity mixed modulation system as described above, or the optical / electric negative feedback loop + addition current value control system for reducing the load on the optical / electric negative feedback loop And the same parts as those shown in FIGS. 15 to 19 are denoted by the same reference numerals.

That is, the semiconductor laser control device 13 according to the present embodiment, as schematically shown in FIG.
It comprises a pulse width generation unit and a data modulation unit 11, a semiconductor laser control unit and a semiconductor laser drive unit (hereinafter simply referred to as a semiconductor laser control unit and a drive unit) 12.

FIG. 1 shows a more detailed configuration example of the semiconductor laser control device 13 in the present embodiment. First, in the present embodiment, a pulse width generation unit and a data modulation unit 11 that generates a plurality of pulses obtained by converting input data into pulse width modulation data and intensity modulation data, a semiconductor laser control unit and a driving unit 12, Most of the components except for some of the components are integrated and configured as a one-chip integrated circuit 20. More specifically, as described later with respect to a part of the circuit configuration, the circuit is formed into one chip using bipolar transistors. Here, the pulse width generation unit and the data modulation unit 11 are not specifically described in detail, but for example, a pulse generation unit having a PLL configuration for generating a plurality of pulses having different timings, and input image data being converted into pulse width modulation data And a data conversion unit including a logical description for converting the data into intensity modulation data, and a pulse width modulation unit for selecting a pulse from the output of the pulse generation unit in accordance with the pulse width modulation data obtained from the data conversion unit. But
The circuit configuration is made up of bipolar transistors for executing these logic descriptions and the like.

Hereinafter, the semiconductor laser control section and the drive section 12 will be described. First, the optical / electrical negative feedback loop 3 includes a light emission command signal setting unit 21 and a light emission command signal generation unit 22 constituting a pulse width modulation / intensity modulation signal generation unit,
It comprises an error amplifier 23 (corresponding to the inverting amplifier 6), a current driver 24, the semiconductor laser 1 and the light receiving element 2. The light emission command signal generation unit 22 includes a light emission command signal generation unit first component unit (denoted as “first light emission command signal generation unit” in the drawing) 22a and a light emission command signal generation unit second unit.
(A second light emission command signal generation unit) 22b. In operation, the current generated by the light emission command signal generation unit first component unit 22a in accordance with the modulated data is compared with the monitor current output from the light receiving element 2 in proportion to the optical output of the semiconductor laser 1. , And the error is converted to an error amplifier 23 and a current driver 24.
The optical / electrical negative feedback loop 3 is formed by converting the current into a forward current of the semiconductor laser 1 through the optical fiber. Here, since the differential quantum efficiency of the semiconductor laser 1 and the light-to-electric conversion light receiving sensitivity of the light receiving element 2 generally vary, the current value must be set according to each characteristic. The light emission command signal setting unit 2
1, a current value I _DA1 , that is, a current value I _DA1 , that is, an external current setting signal is applied so that the semiconductor laser 1 has a desired optical output.
In terms of DC operation, by setting the monitor current value of the light receiving element 2, it becomes possible to absorb individual differences and set the semiconductor laser 1 to always have a desired optical output.

The current driver 24 is configured as, for example, a high-speed voltage shifter 25 that shifts the output of the error amplifier 23 by a desired potential instantaneously in a differential switch configuration. Equivalent to). The voltage shift by the high-speed voltage shift unit 25 instantaneously becomes a forward current of the semiconductor laser 1, and enables high-speed modulation of the optical output of the semiconductor laser 1. In particular, the optical / electrical negative feedback loop 3 includes a high-speed voltage shifter 25 functioning as the current driver 24 in the control system of the optical / electrical negative feedback loop 3.
By having the same output as that of the integrated circuit 20
In the configuration, the number of elements and the power consumption can be reduced.

FIG. 2 shows an example of a circuit configuration using bipolar transistors of the error amplifier 23 and the high-speed voltage shift unit 25. First, at a PD terminal in the light emission command signal generation unit 22 (light emission command signal generation unit first configuration unit 22a), data input by a D / A conversion unit described later in the light emission command signal generation unit 22 is converted into a current I. Convert to _DA1 and light receiving element 2
The result is compared with the monitor current I _PD flowing in proportion to the optical output of the semiconductor laser 1, and the result is detected at the base of the transistor Q _{1 in} the light emission command signal generation unit 22. The result is input to a differential amplifier 41 composed of transistors Q ₂ , Q _3, etc., and the output thereof is output from an LD terminal via a resistor R ₁ to the optical / electrical negative feedback loop 3 which makes a forward current of the semiconductor laser 1. Is composed. Here, the differential amplifier 41 outputs L
While arriving at the D terminal, the transistors Q ₄ and Q ₅ and the resistor R ₂
The high-speed voltage shift unit 25 is configured to instantaneously shift the voltage of the output by a desired potential by a differential switch 42 configured as a differential circuit (corresponding to the invention according to claim 4). ). This voltage shift is a forward current of the semiconductor laser 1 instantaneously through the emitter follower 43 is formed by the transistors Q ₆ to Q ₈ and the like. here,
In the present embodiment, as described above, the driving transistor 7 that finally drives the semiconductor laser 1 and the resistor R _e
DOO has an external relative integrated circuit 20, to the driving transistor 7 resistor R _e, it is necessary to flow a few tens to several hundreds mA current of about to drive the semiconductor laser 1, this embodiment In the case of the configuration as described in the embodiment, the current inside the semiconductor laser control unit and the drive unit 12 is at most several mA at the output unit connected to the drive unit (drive transistor 7), so that the power consumption is reduced. Integration (development of LSI) is facilitated. In the circuit shown in FIG. 2, the resistors R ₂ and R ₃ , the transistor Q _{9, and the} like determine the voltage shift amount of the current driver 24, but the differential quantum efficiency of the semiconductor laser 1 is determined as described above. Since there is an element variation and an efficiency deterioration due to a change with time, the differential quantum efficiency of the semiconductor laser 1 is detected by the differential quantum efficiency detection unit 32, and the voltage shift amount is set. optical output P _S as shown in FIG. 16 (b) can be obtained an ideal light output superimposed. Further, in the circuit shown in FIG.
_2, the differential amplifier 41 constituted by Q ₃ or the like and also forms the output in the resistance R ₄ as voltage drop from the power supply voltage V _cc, optoelectronic negative feedback loop 3 light of the semiconductor laser 1 Since the output is controlled in real time, the power supply voltage fluctuation is also controlled at the same time. In the process of inputting the result of detection at the PD terminal (the base potential of the transistor Q _{1 in} the light emission command signal generating unit first component unit 22 a) via the light receiving element 2 to the differential amplifier 41, the transistors Q ₁₀ , Q
_11, the resistor R and ₄ over feedback through the voltage gain of the differential amplifier 41 is determined by the resistance value of the resistor R _5, R _6, crossover frequency of the differential amplifier 41 by reducing the gain And control speed is improved.

The differential quantum efficiency of the semiconductor laser 1 is detected,
In FIG. 1, a block for realizing the function of setting the amount of voltage shift includes a timing generation unit 31, a differential quantum efficiency detection unit 32, a memory unit 33, and an addition current setting unit 34. As a result, roughly, the timing generation section 31 generates a timing signal sufficiently slower than the control speed of the error amplifier 23, and detects the differential quantum efficiency of the semiconductor laser 1 at that timing by the differential quantum efficiency detection section 32. The detection result is recorded in the memory unit 33, and the current value of the addition current setting unit 34 is set according to the data in the memory unit 33. This operation is performed as an initialization operation only at the time of predetermined initialization such as power-on or reset (when the optical output of the semiconductor laser 1 is turned off), and holds the current value of the addition current setting unit 34 during normal operation.

Further, a power supply unit 61 is provided in the integrated circuit 20 together with a start-up unit 35 connected to the timing generation unit 31.

FIG. 3 shows an example of a circuit configuration using bipolar transistors of the power supply section 61. In the power supply unit _{61, Q 51, Q 52, R} 21, a band gap reference formed in the circuit composed of R _22, R _23, etc., V = (emitter potential -V _BE of Q _{53) V} be; The emitter area and resistance of the transistor are determined so that the base-emitter voltage of the transistor does not change as much as possible with temperature. As a result, a stable potential, each of the emitter potential of the transistor Q _54, Q _55, Q ₅₆ has no temperature characteristics. In the case of the circuit configuration shown in FIG. 3, the current flowing by connecting the resistor R ₂₄ to the emitter of the transistor Q ₅₄ is turned back by the current mirror circuit 63 to generate a current source used in the integrated circuit 20. That is, in the integrated circuit 20, a PNP having a VBBP terminal as a base potential in a start-up unit 35 described later or the like.
All the current flowing through the transistor becomes a constant current source, VBBN
All the currents flowing through the NPN transistors whose terminals are the base potential become constant current sources, and the current value is determined by the resistance connected to the emitter of each transistor.

Next, the startup section 35 will be described. The start-up unit 35 protects the semiconductor laser 1 from deterioration or damage caused by an excessive current flowing through the semiconductor laser 1 until the power supply voltage _Vcc still reaches a predetermined value when the power is turned on. The timing generation section 31 plays a role of generating a required initialization start signal. The start-up section 35 is composed of a first start-up section 35a and a second start-up section 35b as shown in FIG. The second start-up unit 35b will be described later together with the light emission command signal setting unit 21. First, in the first start-up portion 35a, the differential switch 65 constituted by transistors Q _61, Q _62, the power supply voltage V _cc is up to a certain set potential than 0V and the transistor Q ₆₂ is turned on,
Resistor R ₃₁ to _the power supply voltage V _cc exceeds a certain set potential in the range of a predetermined potential the transistor Q ₆₁ is turned on -
Set _R37 etc. In this case, the certain set potential is set as close as possible to a predetermined potential of the power supply voltage _Vcc .
For example, in the case where the predetermined potential of the power supply voltage is 5.0 V, if a certain set potential is set to about 2 to 3 V, it cannot be said that the entire circuit is still operating as desired.
If the voltage is set to about 4.5 V, it can be considered that almost the entire circuit is performing a desired operation, and the protection of the semiconductor laser 1 and the generation of the initialization start signal can be performed more safely. The first start-up unit 35a corresponds to a start-up unit according to claim 9.

[0050] Specifically, the base potential of the transistor Q ₆₂ is only that the collector potential of the transistor Q ₆₃ and the voltage shift through the emitter follower 66, the base potential of the transistor Q ₆₂ by the collector potential of the transistor Q ₆₃ It is determined. Similarly, the base potential of the transistor Q ₆₁ is determined by the collector potential of as long as the transistor Q ₆₅ of the transistor Q ₆₄ is turned off. The collector potential of the transistor Q ₆₃ is more determined current and supply voltage of the current source formed by the transistor Q ₆₆ and the resistor R _33, I the current in the composed current source transistors Q ₆₆ and the resistor R _{33 1,} when the power supply voltage is V _cc, the collector potential V _Q63c of the transistor Q ₆₃ becomes _{V q63c = V cc -I 1 *} R 31. Here, since the current I ₁ is a constant current source having VBBN as a base potential, I ₁ * R ₃₁ is a constant potential. Originally, the power supply section 61 is also composed of the power supply voltage. Therefore, if the power supply voltage is 0 V, the current I ₁ is also 0. However, since a certain set potential is set as close as possible to a predetermined potential of the power supply voltage, In a state (time) in which the differential switch 65 composed of the transistors Q ₆₁ and Q ₆₂ switches, it is assumed that the power supply unit 61 functions sufficiently and the current I ₁ is also a constant current. . Then, _Vq63c changes according to the power supply voltage _Vcc .

The collector potential V of the transistor Q _65
Q65c, like the above equation, the current source of the current composed of the transistors Q ₆₇ and the resistor R ₃₄ When I _2, the _{V q65c = V cc -I 2 *} R 32. Here, considering the current through the resistor R ₃₆ as resistor _R 34, R ₃₅ have equal resistance values, and _{V cc = (I 2 + I} 3) * R 36 + V be + I 2 * R 35. Here, the current I ₃ is determined by the transistor Q ₆₈ and the resistor R
The current value of the constant current source constituted by the _37, V _BE is the base-emitter voltage of the transistor.

[0052] From the above equation, the _{V q65c = I 3 * R 36} + V be + I 2 * (R 36 + R 35 -R 32). Here, since I ₃ * R ₃₆ has a constant potential similarly to the current I ₁ and V _be also has a substantially constant potential, if R ₃₆ + R ₃₅ = R ₃₂ , the collector potential V _q65c of the transistor Q ₆₅ is equal to the power supply. A constant potential independent of voltage can be obtained. That is, the collector potential V _Q65c of the transistor Q ₆₅ is constant potential, the collector potential V _Q63c of the transistor Q ₆₃ is changed in accordance with the supply voltage V _cc, by setting both the potential appropriately, the power supply voltage at power-on Switch 65 composed of transistors Q ₆₁ and Q ₆₂ in accordance with the change of
Can be switched at an appropriate timing. As a result, _the power supply voltage V _cc is up to a certain set potential than 0V, that is, in the state where the transistor Q ₆₂ is turned on, the collector current flowing through the transistor Q ₆₂ is inverted by the current mirror circuit 67, the transistors Q _69, Q
₇₀ turns on, forcing the potentials of the TDSTART terminal and the PD terminal to approximately the same potential as _Vcc . Specifically, the output of the error amplifier 23 is forcibly set to the L level by forcibly setting the potential of the PD terminal of the light receiving element 2 to the H level, so that the forward current of the semiconductor laser 1 does not flow. The suppression protects the semiconductor laser 1. At the same time, as described later, the potential of the TDSTART pin is forcibly set to H level.
By setting the level, the oscillation circuit in the timing generation section 31 is suppressed so as not to forcibly oscillate. And
Power supply voltage V _cc is equal to or greater than a certain set potential, that is, the transistor Q ₆₁ is changed to the ON state, the semiconductor laser 1
Is released, the normal operation state is obtained, and the oscillation start signal is obtained by canceling the oscillation suppression of the oscillation circuit in the timing generation section 31. At the same time, the VPTDSTART terminal potential for generating the current source of the timing generator 31 is output.

The timing generation section 31 can be constituted by using, for example, a delay circuit. Have been. Schematically,
The oscillating signal generated in the oscillating circuit 36 is latched by the latch circuit 37, and the latched data is sequentially transmitted to the next stage to generate, for example, six timing signals T0 to T5. The oscillation circuit 36 is forcibly suppressed from oscillating. The differential quantum efficiency detector 32 includes, for example, a sample and hold circuit 38 for detecting a peak value in an error output of the error amplifier 23,
8 and a comparator 39 for comparing the output value of E.8 with a predetermined value. The memory unit 33 has a function of holding the comparison result of the comparator 39 in synchronization with timings T1 to T5 generated by the timing generation unit 31.
The addition current setting unit 34 includes, for example, a 5-bit D / A
It consists of a converter. The timing generator 31, the differential quantum efficiency detector 32, the memory 33, and the addition current setting unit 34 are also integrated by bipolar transistors.

Therefore, first, the timing generator 31
FIG. 5 shows an example of a circuit configuration using a bipolar transistor of the oscillation circuit 36 in FIG. FIG. 8 shows a schematic operation at the time of initialization. Collector potential V _Q22C transistor Q ₂₂ is represented as an oscillation operation in FIG. 8, the collector current of the transistor Q ₂₂ is, the transistor Q _24, Q
It is turned on and off by a differential switch 46 composed of ₂₅ ,
When the collector current of the transistor Q ₂₂ is larger than the collector current of the transistor Q ₂₁ when turned on, the collector potential V _Q22C transistor Q ₂₂ is oscillated by the respective current repeated charge the capacitor C _1, the discharge I do.

First, at timing 0 shown in FIG.
From the time when the power is turned on until the oscillation start timing signal TS is sent from the start-up unit 35, TD
The potential of the START terminal is forced to H level (almost Vcc
Since the VPTDSTART terminal is at 0 V, the transistor Q ₂₃ generated from the VPTDSTART terminal
The collector current is zero, but the differential switch 46 also transistor Q ₂₅ is at the L level, the collector current of the transistor Q ₂₃ is 0, and has a collector current is also 0 of the transistor Q _22.

Here, referring to FIG. 7 showing the configuration of the last stage of the latch circuit 37, the potential of the VPTDSTART terminal is 0 V,
The collector current of the transistor Q ₃₁ is 0A. As a result, the base potential of the transistor Q ₂₃ is V _cc, the collector current of the transistor Q ₂₃ becomes 0A. Further, in the differential switch 46, the collector current of the transistor Q ₂₃ is 0A, the base potential of the transistor Q ₂₅ is L level, the collector current of the transistor Q ₂₂ 0
A.

[0057] After that, past the oscillation start timing signal TS, the beginning collector current of the transistor Q ₂₂ flows,
Since the differential switch 46 transistors Q ₂₅ is L level, the collector current of the transistor Q ₂₃ is turned back by the current mirror circuit 47 by transistor Q _22, Q _26, the collector current of the transistor Q _22.
This timing TS, since the current of the power supply unit 61 is 0, the transistor when the collector current of the transistor Q ₂₂ is greater than the collector current of the transistor Q ₂₁ is Q
₂₂ collector potential V _Q22C , that is, the TDSTART terminal potential is
Decreases gradually. Then, at the moment when the base potential of the transistor Q ₂₄ is equal to or lower than the base potential of the transistor Q ₂₅ , the differential switch 46 operates, the transistor Q ₂₄ is turned on, and the collector current of the transistor Q ₂₆ , the collector current of the transistor Q ₂₂ is turned off, the base potential of the transistor Q _25, the transistor Q
It increases the potential amount determined by the collector current of ₂₄ and a resistor R _11. This moment is timing T0.

[0058] Beyond the timing T0, the collector current of the transistor Q ₂₂ is turned off, transistor Q
₂₂ collector potential V _Q22C , that is, the TDSTART terminal potential is
Gradually rise. Then, the moment the base potential of the transistor Q ₂₄ rises above or base the same potential of the transistor Q _25, and inverted differential switch 46 repeats the oscillation operation of the collector current of the transistor Q ₂₂ is turned on. The amplitude of the oscillation is determined by the potential determined by the collector current of the transistor Q ₂₄ and the resistor R _11, the period is determined collector current of the transistor Q _21, the collector current of the transistor Q _22, the capacitance of the capacitor C _1, these By properly determining the value of, a desired timing signal can be obtained.

In such an operation, the transistor Q
When ₂₂ of the collector current of just 2 times the collector current of the transistor Q _21, and the collector current of the transistor Q _21,
(Collector current of the transistor Q ₂₂₎ - and becomes a current (collector current of the transistor Q ₂₁₎ are equal, the charge in the capacitor C _1, the charge amount per unit time is discharged are equal, as shown in FIG. 8 What
A triangular wave having the same rise time and fall time is obtained.

[0060] square wave is obtained to the base of the transistor Q ₂₅ as an oscillation output of such an oscillation circuit 36, after the voltage shift, swing amount adjustment, reversal becomes the processing has been performed, FIG. 8
The output waveform of the emitter potential V _QXE of the transistor Q _X shown in FIG.

Next, FIG. 6 shows an example of a circuit configuration of a latch circuit 48, which is a constituent unit of the latch circuit 37. In the present embodiment, the latch circuit 37 is configured by connecting the latch circuits 48 in six stages in order to generate the timing signals T0 to T5. Is shown.
In the illustrated example, it is constituted a plurality of transistors, a resistor as a component, among the, transistors Q ₃₁ ~
Q ₃₃ in forming a single switch 49a, also forms a single switch 49b in transistor Q ₃₄ to Q _36. Wherein the switch 49a, when the collector current of the transistor Q ₃₃ is turned on, the base potential of the transistor Q _31, that is, by the inverted output data to the base potential and the emitter potential of the transistor Q _37. Further, the switch 49b, the collector current of the transistor Q ₃₆ is when on, the base of the transistor Q ₃₄ is connected to the emitter of the transistor Q _37, the operation of directly holding the output.

[0062] The base of the transistor Q ₃₃ CLK, based on / CLK of the transistor Q ₃₆ (with respect to the signal, "/" indicates inversion), the base of the transistor Q ₃₁ DATA0, as the output Q of the emitter of the transistor Q _37, When these relationships are represented by logical expressions, Q = CLK.DATA0 + / CLK.Q

Here, as described above, the transistor Q _X
The emitter potential V _QXE of FIG. 8 (that is, the base / CLK of the transistor Q ₃₆ ) is in an output holding state at H level from the timing TS to the timing T 0, and is composed of the transistors Q ₃₈ , Q _{39 and the} like. Since the current source 50 uses VPTDSTART from the start-up unit 35 as a base potential, the current flows from the moment when the current reaches 0 and reaches the timing TS until the timing TS, so that the output Q is at the H level until the timing T0. . Timing T
0 becomes the output Q is the first time L level, since the timing T0, the base of the transistor Q ₃₁ (input data)
Is at the L level, the output Q maintains the L level. This state is shown as the waveform of the emitter potential V _{Q3 7E} transistor Q ₃₇ in FIG. 8 (a timing signal T0).

In the next stage (not shown), CLK is inverted and input.
_Assuming that the emitter potential V _Q37E of the transistor Q ₃₇ is DATA1, the timing signal T1 indicated by V _{Q37 (1) E} in FIG. 8 can be obtained by _setting Q ′ = / CLK · DATA1 + CLK · Q ′.

Hereinafter, timing signals T2 to T5 can be similarly obtained. “N” at V _{Q37 (n) E} in FIG.
Indicates the number of stages 1 to 5.

Further, as shown in FIG. 7, in the last-stage latch circuit 48 _L for generating the timing signal T5,
The collector current of the transistor Q ₃₁ are given to the base of the transistor Q ₂₃ in the oscillation circuit 36, an oscillation circuit 3
6 drive voltage. Therefore, the timing T from the base potential timing TS of the transistor Q ₂₃
Up to 5 are supplied. However, the base potential of the transistor Q ₂₃ is not supplied with turning off the collector current of the transistor Q ₂₃ at the moment when the timing T5.

That is, the oscillation circuit 36 oscillates only during generation of a necessary timing signal, and stops oscillating at the same time when the generation of the desired timing signal is completed. The circuit configuration has no adverse effect. Further, in order to generate the timing signals T0 to T5 as described above, it is possible to use a delay circuit or the like, but as in the present embodiment,
By configuring with the oscillation circuit 36, only, even when generating a plurality of timing signals by the capacitors C ₁ and LSI (integrated circuit 20) outside the external elements, the timing of the oscillation circuit 36 Can be set freely. However, when the timing generation unit 31 is configured using a delay circuit, an external element for determining each timing is required to freely set the timing, but when the number of required timings is small, Using a delay circuit has the advantage that a latch circuit is not required. In any case, the control speed of the optical / electrical negative feedback loop 3 can be freely set, and the semiconductor laser 1 and the light receiving element 2
It is also possible to obtain an optical output waveform which is not affected by the frequency characteristics of the integrated circuit 20, which is convenient for optimizing the initialization time of the integrated circuit 20.

In general, a frequency characteristic exists between the semiconductor laser 1 and the light receiving element 2, and this frequency characteristic is used for the operation of the control system (optical / electrical negative feedback loop 3) and the timing setting. There is no problem if the characteristics are good and there is no effect, but if the frequency characteristics are not good, if the above-mentioned timing is constant, the distance between the semiconductor laser 1 and the light receiving element 2 It is necessary to add a circuit for compensating the frequency characteristic or set the timing so as to be sufficiently delayed. However, if such timing is set sufficiently late, the initialization time will be prolonged accordingly. However, if a frequency characteristic compensation circuit is added, the number of elements will increase, which is not preferable in any case. In this respect, as in the present embodiment, by configuring the timing generation unit 31 using the oscillation circuit 36 does not require a circuit for compensating the frequency characteristics by simply changing the capacitance of the capacitor C _1, In addition, since all the initialization times do not become long, efficient initialization can be performed while reducing the number of elements. Further, when a timing signal is generated using such an oscillation circuit 36, a flip-flop is usually used, but by using a latch circuit 37 in which a required number of latch circuits 48 are combined as in this embodiment. , The number of elements can be reduced.

Next, a schematic operation at the time of initialization controlled by these timing signals will be described with reference to a time chart of FIG. 8 and an example of a circuit configuration of the differential quantum efficiency detector 32 shown in FIG. First, the optical output of the semiconductor laser 1 is set to a desired maximum emission state from the off state forced at the timing TS. It is assumed that the maximum light emission value has already been set in the light emission command current generation unit 22. Then, at the timing T0, the input data is set to all 0s to set the offset light emission state, and after maintaining this state until the timing T5, the normal operation state for receiving the original input data is set after the timing T5. In order to operate the optical / electrical negative feedback loop 3, it is necessary to perform offset light emission in which the light output of the semiconductor laser 1 is slightly turned off without completely turning off the light output. Is controlled by the optical / electrical negative feedback loop 3 between the set maximum light emission and offset light emission.

The optical output of the semiconductor laser 1 is always detected at the time of initialization, that is, at power-on or reset release, by detecting the differential quantum efficiency by executing a sequence operation as shown in FIG. Set an appropriate addition current value.

The difference between the maximum light emission and the offset light emission as shown in FIG. 8, that is, the operating current Iop−the oscillation threshold current I
Since th is the differential quantum efficiency, the differential quantum efficiency detection unit 3
The difference is detected by the sample-and-hold circuit 38 in 2. Schematically, this difference corresponds to the difference between the potentials of the terminals of the resistor R _e (see FIG. 2) between the maximum light emission and the offset light emission. When the voltage shift unit 25 serving as the current driver 24 is not operating, the difference depends on the difference between the emitter potentials in the two cases of the transistor Q ₉ (see FIG. 2) of the current driver 24. Therefore, the emitter potential of the transistor Q ₉ in the maximum emission is sampled and held, 0 at the timing T0
The potential shift amount of the voltage shift unit 25 was gradually changed by adding the current setting unit 34, the difference, to detect the differential quantum efficiency by the potential change of the resistance R _e of the voltage shift unit 25.

[0072] In detail, the emitter potential of the transistor Q ₉ as shown in FIG. 8, i.e., the transistor VCOMP terminal via an emitter follower 51 of the transistor Q ₄₂ Q ₄₃
At the base potential. During this base potential of the transistor Q ₄₃ is that the current of the current source 52 constituted by the transistors Q ₄₅ and the like flows through the transistors _{Q 41, Q 46, Q 47} , Q
The voltage follower 53 consists of ₄₈ such as the base potential and the same potential of the transistor Q _44. Timing T
When the current of the current source 52 is turned off at 0, the transistor Q
Change in the base potential of ₄₃ indicates as a potential change of the VCOMP terminals which the base potential of the transistor Q ₄₄ is not changed larger the capacitance of the capacitor C _2, the base potential of the transistor Q ₄₃ in the timing T0, that is, the maximum emission At this time, the emitter potential of the transistor Q ₉ (see FIG. 2) can be sampled and held. The lower part of FIG. 8 shows a schematic waveform sampled and held by these transistors Q ₄₃ and Q ₄₄ .

The base potentials of these sampled and held transistors Q ₄₃ and Q ₄₄ are changed to transistors Q ₄₉ and Q ₅₀
And the like, and compares the magnitudes with each other.
Hold at 3. Accordingly, the memory unit 33 is not particularly shown in the configuration example, but may have a function capable of holding the comparison output of the comparator 39 in synchronization with the timing signals T1 to T5. constituted by five stages of the latch circuit as used in the base potential of the transistor Q ₄₃ side in the comparison of the comparator 39 is the transistor Q ₄₄
What is necessary is just to comprise so that L level may be output, when it is higher than the base potential of the side.

The addition current setting section 34 adds five switches composed of two-stage differential switches, a current mirror circuit for supplying a current to the current sources of these switch sections, and an output of each switch section. And a current mirror circuit that outputs the current from the current driver (high-speed voltage shifter 25). Here, basically 5-bit D / A converter is constituted by five switching unit, a current source of these switch portions, when the minimum bit current and I _1, the switch portion of the next bit 2 * I ₁ , and 4 * I ₁ , 8 * I ₁ , 16 * I ₁ for each higher-order bit switch unit. Thus, next to the maximum 31 * I ₁ as an output current of the entire switch unit, when this, the maximum current (maximum voltage) set in the current driving portions (voltage shift unit 25), the aforementioned (operating current Iop) - (Oscillation threshold current Ith) is set to be larger than the maximum value.

Here, at the timing T0, as shown in FIG. 8, the light output of the semiconductor laser 1 is changed from the maximum light emitting state to the offset light emitting state, and at the same time, the current of the most significant bit of the switch section is forcibly output. In this state, since the maximum light emitting state is shifted to the offset state and the current of the switch unit of the most significant bit is forcibly output, the potential between the terminals of the voltage shift unit also changes. The control system 3 controls the optical output of the semiconductor laser 1 so as to be in the offset light emission state. Such a change is detected by the differential quantum efficiency detection unit 32 and its output is compared with the maximum light emission state.
To be stored. The result is stored in the memory unit 33 at the timing T
At 1, the latch section is reset, and the switch section of the most significant bit of the addition current setting section 34 is reset. Here, the timing T1-T0 needs to be set to a time during which the control system of the optical / electrical negative feedback loop 3 sufficiently converges.

At the timing T1, the timing T0
As in the case of, the upper 2 bits are forcibly output, and
The result is reset at timing T2. In the present embodiment, the differential quantum efficiency is detected with an accuracy of D / A for 5 bits, so that the same is repeated for 5 bits.
To illustrate how the change of the base potential at this time, the same as in the case of a base potential of the transistor Q ₄₄ shown in the lower portion in FIG. The illustrated example in this case shows a waveform in the case of 1,1,1,0,1 in order from the lower bit.

In this embodiment, the differential quantum efficiency detector 3
2 and the detection accuracy of the addition current setting unit 34 are 5 bits. However, if the detection accuracy is increased by further increasing the number of bits, the light output amount corresponding to P _S in the light output waveform shown in FIG. And the amount of control of the optical output by the control system including the optical / electrical negative feedback loop 3 is reduced, and the optical output waveform approaches a more ideal square wave.

Next, FIGS. 10 to 12 show circuit configuration examples using bipolar transistors of the light emission command signal setting unit 21 and the light emission command signal generation unit 22 constituting the pulse width modulation / intensity modulation signal generation unit. FIG. 10 shows the light emission command signal setting unit 21 and FIG.
2a and FIG. 12 show the light emission command signal generation unit second configuration unit 22b.

First, the configuration of the light emission command signal setting unit 21 includes a current setting of the light emission command signal generation unit 22, a current setting of the addition current setting unit 34, a base current compensation unit for the current of the light emission command signal generation unit 22, and , The current of the light emission command signal generating section 22 and the current of the addition current setting section 34 are adjusted in accordance with an external signal, and each section will be described with reference to a circuit example shown in FIG.

[0080] current setting of the light emission command signal generating unit 22 is performed by the emitter potential of the transistor Q ₇₁ and the resistor R _41. Here, the current of the light emission command signal generation unit 22 is:
Since the direct current is a monitor current of the light receiving element 2, the current needs to be a current that is not affected by a temperature change inside the integrated circuit 20 (LSI). That is, the emitter potential of the transistor Q ₇₁ is stable potential, the resistance R ₄₁ should be a required resistance of absolute accuracy. Therefore, the emitter potential of the transistor Q ₇₁ is produced via the configured voltage follower 71 VREF11 terminal potential is generated stable potential at the power supply unit 61 in the transistor Q ₇₂ to Q ₇₅ or the like, the terminal as an external terminal , a resistor R ₄₁ absolute accuracy, and good external resistor or a variable resistor of the temperature characteristics. Here, the resistance R ₄₁ corresponds to the external device refers to the invention of claim 2 or 11, wherein. By changing the resistance value of the resistor R ₄₁ in accordance with the characteristics of the semiconductor laser 1 and the light receiving element 2 can be adjusted to obtain a desired light output.

[0081] transistor Q ₇₁ relative to the emitter potential of the current setting of the added current setting unit 34 transistors Q _71, Q
_76, via the Q ₇₇ was determined by the emitter potential of the transistor Q ₇₈ to be substantially the same potential as the emitter potential of the transistor Q ₇₁ and the resistor R _42, and outputs from IDA2SET terminal to the addition current setting unit 34.

[0082] base current compensator of the current of the light emission command signal generation unit 22 is performed by the base current of the transistor Q _77. Current of the light-emitting instruction signal generating unit 22, it is necessary an absolute current determined by the external light receiving element 2 as described above, for example, in the circuit configuration shown in FIG. 10, the emitter potential of the transistor Q ₇₁ a resistor after the reference current determined by the R ₄₁ is the absolute current but that its current is inverted by the current mirror circuit 72, for example, the current in the light emission command signal generator 22 through the least significant bit, the switch transistor Since current is drawn from the PD terminal via Q _{81 to} Q ₈₃ , a base current error of each transistor occurs due to passing through three of these switch transistors. The same applies to other bits as well as the least significant bit. Such a base current error in order to compensate for adjusting the base current of the transistor Q _77.

[0083] taking the case of the least significant bits as an example, for specifically expressed by the formula, the emitter current I _ref of the transistor Q _71, the base current I _Q77b transistor Q _77, the base current I _Q81b of the transistor Q ₈₁ , Transistor Q ₈₂
Base current corresponding to the least significant bit current of _Iq82b5 ,
A base current corresponding to the least significant bit current of the transistor Q ₈₃ and I _Q83b5, in a state where the least significant bit current is flowing in this path, if the current in the current mirror circuit 72 is ideally reversed , The current I of the light emission command signal generation unit 22 corresponding to the least significant bit current
_{DA1 5 is, I DA1 5 = (I ref} + I q77b) / 4-I q81b -I q82b5 -
_Iq83b5 . Here, the collector current I _c flowing through the transistor Q ₈₁ to Q _83, as described above, can be approximated as _{I c = (I ref + I} q77b) / 4. Also, the base current _Ib and the collector current I
relationship with _c, when the current amplification factor and h _fe, since it is _{I c = h fe · I b} , is approximated with _{I q81b = I q82b5 = I q83b5} , I DA1 5 = (I ref + I q77b) / 4- (3 / h _fe ) (I _ref
+ I _q77b ) / 4. Here, (3 / h _fe ) (I _q77b / 4) = (3 / h _fe ) (1/4) (I _c
/ H _fe) next, when sufficiently small relative to _{I c, I DA1 5 = (} I ref + I q77b) / 4- (3 / h fe) (I ref
/ 4). Here, in order to be I _{DA1 5} = I _ref / 4 is required to be _{I q77b / 4 = (3 /} h fe) (I ref / 4). That is, the emitter current of the transistor Q ₇₇ by passing 3 times the emitter current I _ref of the transistor Q _71, it can be a _{I DA1 5 ≒ I ref / 4} . Therefore, base current compensation of the switch transistor that passes can be performed.

Further, by this compensation, the base current compensation is simultaneously performed for all the bits. For example, next consider the most significant bit and _let the base current of transistor Q84 be I
_Q84b, the base current corresponding to the most significant bit current I _Q82b1 transistor Q _82, when the base current corresponding to the most significant bit current of the transistor Q ₈₃ and _{I q83b1, I DA1 1 = (} I ref + I q77b) · 4 −I _q84b −I _q82b1 −
I _Q83b1 next, as in the case of the _I q84b = I q82b1 = I
is approximated with _{q83b1, I q77b · 4 = (} 3 / h fe) · I ref · 4 next, again by passing 3 times the emitter current I _ref of the transistor Q ₇₁ and the emitter current of the transistor Q _77, I _{DA1 1} ≒ I _ref · 4, and it can be seen that base current compensation of the switch transistor passing through can be performed. In other words, in the case of the circuit configuration of the present embodiment, the generation of the error current and the characteristic change due to the base current are suppressed by adding the reference current by the number of switch transistors passing through the base current of the reference current. And base current compensation can be easily performed. The base current compensator 73 having such a function corresponds to the base current compensator according to the tenth or eleventh aspect of the present invention.

Next, a description will be given of a portion in which the current of the light emission command signal generation section 22 and the current of the addition current setting section 34 are adjusted in accordance with an external signal in conjunction with each other. As described above, the current setting of the light emission command signal generator 22 and the current setting of the added current setting unit 34 is determined by the emitter potential of the transistor Q ₇₁ and the resistor R _41, also as described above transistor Q
The emitter potential of the ₇₁ inputs the VREF11 terminal potential, formed by the transistors Q ₇₂ to Q ₇₅ such voltage follower 7
While a first output, by adopting a configuration for inputting a control voltage from VCONT terminal via a resistor R _43, R _44, transistor Q ₇₉ in parallel with VREF11 terminal, the emitter of the transistor Q ₇₁ by this control voltage Change the potential. That is, the current of the light emission command signal generation unit 22 and the current of the addition current setting unit 34 can be increased and decreased in conjunction with each other.

[0086] For example, when the resistance value of the resistor R _44, R ₄₅ are equal, becomes equivalent to the potential V _VCONT of VREF11 potential V _{VREF 11} and VCONT Pin, the emitter potential V _Q71e of the transistor Q ₇₁ is V _q71e = (V _VREF11 + V _VCONT ) / 2 For example, the potential V _VREF11 is _set to 1 [V] and the potential V
_VCONT the moving 0-2 [V] When the emitter potential V _Q71e of the transistor Q ₇₁ becomes possible to move 0.5 [V] to 1.5 [V].

FIG. 13 shows a schematic waveform in this case. In general, in a laser printer or the like, when the light output of the semiconductor laser 1 is subjected to scanning exposure on a photoconductor or the like via a polygon mirror or the like, due to the influence of a change in the distance to the photoconductor or the shape of a converged beam, There is a need to dynamically finely adjust the optical output of the semiconductor laser 1 to perform shading in a so-called optical system and to correct the shading, or to finely adjust the light amount when setting the light amount. FIG.
FIG. 13A shows an optical output waveform in an initial state, and FIG.
(C) shows an optical output waveform when the current of the light emission command signal generation unit 21 is changed during operation. In any case, a steady output is desired by control by the control system (optical / electrical negative feedback loop 3). However, if the current of the light emission command signal generation unit 22 is merely increased at the time of rising, the waveform becomes dull as shown in FIG. If only is reduced, an overshoot waveform will result). In this regard,
As described above, when the current of the light emission command signal generation unit 22 and the current of the addition current setting unit 34 are increased and decreased in conjunction with each other,
The result is as shown in FIG. That is, the current set value in the added current setting unit 34 changes in conjunction with the current setting.
In the above-described shading correction and fine adjustment of the optical output of the semiconductor laser 1, no matter how the VCONT terminal is moved, the control amount of the control system as shown in FIG. Can be obtained.

Now, the second start-up section 35a will be described in relation to the light emission command signal generating section 21. Emitter potential V of the transistor Q ₇₁ as described above
_q71e is an output of the voltage follower 71, and its control speed and stability are controlled by the capacitor C ₃ (see FIG. 10). will be the emitter potential of the transistor Q ₇₁ is set such the added current setting unit 34 before the desired value is carried out, possibly optical output of the semiconductor laser 1 can no longer become a desired value and the light output is there. The second start-up section 35a is provided to solve this problem, and includes a transistor Q
The emitter potential of ₇₁ , that is, the potential of the VR terminal exceeds a certain set potential (the voltage follower 71 enters an operating state).
Up, without starting the timing generator 31 as in the first start-up portion 35a, is configured to activate the first timing generator 31 to the emitter potential VR of the transistor Q ₇₁ has reached a certain set potential. Such a second start-up unit 35b corresponds to the start-up unit according to the present invention. FIG.
In the start-up unit 35 shown in (1), the first start-up unit 35a and the second start-up unit 35b are AND-connected, and both the power supply voltage _Vcc and the current of the light emission command signal generation unit 21 are Initialization and the operation of all circuits are started only when both become the desired states. Here, the invention according to claim 17 is configured.

Next, the light emission command signal generator 22 will be described. The light emission command signal generation unit 22 has 5 bits (b
0, b1, b2, b3, b4) and a current addition drive unit, and further include a current compensation unit for the light emission command signal generation unit 22 and an offset current generation unit. The light emission command signal generation unit 22 includes two 5-bit D / D
A light-emitting command signal generator first component 22a and light-emitting command signal generator second component 2
2b.

However, if it is desired to set the light output with higher accuracy for the first component 22a of the light emission command signal generator, the number of bits of the D / A converter may be increased.
Alternatively, if pulse width modulation is mainly used, D /
The number of bits of the A converter may be reduced. Further, as for the current generation method, the current inversion by the current mirror circuit and the resistance ladder type D / A may be combined as shown in the illustrated example.

The current addition drive section detects the current I _DA1 and its inverted current with the emitter potentials of the transistors Q ₈₁ and Q ₈₂ , respectively, and after passing through the emitter followers Q ₈₃ and Q ₈₄ , the error amplifier 23 and the current drive The signal is input to the bases of transistors Q ₄ and Q ₅ constituting the differential switch 42 in the unit 24.
Since the emitter potentials of the transistors Q ₈₁ and Q ₈₂ reflect the current value of I _DA1 as they are, the differential switch 42 composed of the transistors Q ₄ and Q ₅ is not a binary output of on / off. , D / A with 5 bits, a 5-bit current drive output can be obtained at high speed.

Further, the light emission command signal generation unit second component unit 22
“b” has the same 5-bit D / A configuration as the light emission command signal generation unit first configuration unit 22a, and outputs the lowest potential that determines the current source to the outside as a DA1GND terminal. This is because normally only one D / A of the light emission command signal generating unit first component unit 22a is sufficient, so that the DA1GND terminal is opened (open).
Light emitting command signal generating section second constituent section 2 having a 5-bit configuration
2b is not operated. Alternatively, the light emission command signal generation unit second configuration unit 22b may be omitted from the beginning, but the variation range of the monitor current of the light receiving element 2 is large, or
If the current range set by the light emission command signal generation unit 22 is large to be used for various light receiving elements 2 (or the semiconductor laser 1), an excessively large current change may occur in one D / D.
In the case of A, there is a problem that the linearity of D / A is deteriorated and an error current is generated. For this reason, a 5-bit light emission command signal generation unit second configuration unit 22b is added. Further, when a further dynamic range is required, three or more D / A configurations may be provided in parallel. The invention according to claim 12 is configured here.

Next, the current compensator in the light emission command signal generator 22 will be described. This current compensator, unlike the current compensator (compensates for the current subtracted from the current I _DA1 ) in the light emission command signal setting unit 21, compensates for the current added to the current I _DA1 . That is, the transistors Q ₁ and Q ₈₃
Is the base current compensation. Taking the transistor Q ₁ as an example, the emitter potential of the transistor Q ₁ is because the collector current of the transistor Q ₈₅ which forms the current source underneath, the base current of the transistor Q ₁ is substantially the same as the base current of the transistor Q ₈₅ Yes, flowing a base current of the transistor Q _85, the PD terminal is inverted by the current mirror circuit 81 constituted by transistors Q _86, Q ₈₇ or the like.

When these relationships are expressed by using equations, N
The current amplification factor of the PN transistors h _fen, the h _fep current amplification factor of the PNP transistor, the base current i _b of the transistor Q _1, the collector current of the transistor Q ₈₇ if I, first, the emitter current of the transistor Q ₁ i ₁
Is i ₁ = a _{(1 + h fen) · i} b, a base current i ₂ of the transistor Q ₈₅ becomes _{i 2 = (1 + h fen} ) · i b / h fen. By this current through the current mirror circuit 81 constituted by transistors Q _86, Q ₈₇ or the like, the collector current of the transistor Q ₈₇ becomes _{I = i b / {1+ (} 2 / h fep). For example, if the current amplification factor h _fep is 100,
Since I ≒ 0.98i _b , I without the compensation circuit
Considering that _DA1 current error of an i _b, it can be seen that error becomes 1/50. It can be compensated in a similar circuit configuration for the base current of the transistor Q _83.

[0095] Further, if you want to increase the accuracy of the compensation, by using the base current compensating current mirror circuit, since the _{I = i b / {1+ (} 2 / h fep 2), further 1 error / It can be reduced to 50 (when h _fep is 100).

Further, the offset current generator will be described. As described above, in order to control the optical output of the semiconductor laser 1 in real time in the optical / electrical negative feedback loop 3, the optical output of the semiconductor laser 1 cannot be made completely zero. It is necessary to set the minimum value of the light output of 1. The setting of the minimum value is performed by the offset current generation unit, and the power supply unit 6 shown in FIG.
1, the light emission command signal generator 2 shown in FIG.
2b, offset current generators 82 and 83 for setting the offset current are provided. The offset current generated by these offset current generators 82 and 83 is compared with the monitor current of the light receiving element 2 at the PD terminal, and becomes the forward current of the semiconductor laser 1 by the error amplifier 23. Can be set.

[0097] First, the offset current generator 82 in the power supply unit 61 shown in FIG. 3, the transistor Q ₅₆ and the resistor R ₂₅
Is constituted by a, the integrated circuit 20 as the emitter potential of the transistor Q ₅₆ is described in the power supply unit 61
This is a stable potential in the (LSI), and a desired current can be externally set by making the resistor R _{25 an} external resistor or a variable resistor. The resistor R ₂₅ corresponds to the external device refers to the invention of claim 6 or 8, wherein.

The light emission command signal generator second component 22
offset current generation unit 83 in b, the transistor Q ₈₈
It is composed of and the resistance R _51, the resistor R ₅₁ by an external resistor or a variable resistor, can be set from outside the desired current. This resistor _R51 also corresponds to the external element according to the invention of claim 6 or 8. The base potential of the transistor Q ₈₈ is because it is the current setting portion in emission command signal generator 22 is preset to match the monitor current characteristics of the light receiving element 2 potential, in the case of large light-receiving element of the monitor current is The offset current generated by the offset current generation unit 83 also increases, and in the case of a light receiving element with a small monitor current, the offset current generation unit 8
The offset current can be set in conjunction with the current setting unit in the light emission command signal generation unit 22 so that the offset current generated in 3 is also small. Such a function,
It corresponds to the interlocking setting unit according to the invention of claim 7 or 8,
The maximum current and the offset current of the light emission command signal generation unit 22 are set in conjunction with each other.

As described above, the current obtained by adding the currents generated by the two offset current generators 82 and 83 becomes the offset current, so that the external resistors R ₂₅ and R ₅₁ are set to appropriate resistance values in advance. By doing so, it is possible to obtain a desired offset emission of the semiconductor laser without setting an offset current each time in accordance with the monitor current characteristic of the light receiving element 2, and thus the adjustment process can be automated.

In this embodiment, a 5-bit D / A
The light emission command signal generation unit 22 is configured by separately providing two components as a light emission command signal generation unit first configuration unit 22a and a light emission command signal generation unit second configuration unit 22b, but as illustrated in FIG. The D / A configuration described above may be made common and configured as a light emission command signal generation unit 91 as one circuit (corresponding to the invention according to claim 5). According to this, the parts that perform the same function are shared,
The number of elements constituting a circuit can be reduced.

In the present embodiment, the description has been given of an example in which most of the semiconductor laser control device 13 is integrated as an integrated circuit 20 using bipolar transistors. However, the present invention is not necessarily limited to an integrated circuit using bipolar transistors. -It may be one using a MOS transistor, a combination of both, or the like, and further applicable to a non-integrated configuration.

[0102]

According to the first aspect of the present invention, a pulse width modulation / intensity modulation signal for generating a light emission command signal for simultaneously performing pulse width modulation and intensity modulation on the input data based on the input data. A generating unit, a semiconductor laser, and a light receiving signal proportional to the light output of the semiconductor laser obtained from the light receiving element by forming an optical / electrical negative feedback loop together with a light receiving element for monitoring the light output of the semiconductor laser; A sum or difference between an error amplifier for controlling the forward current of the semiconductor laser so that the emission command signal given from the width modulation / intensity modulation signal generator is equal to the control current of the optical / electrical negative feedback loop; A drive current generated in accordance with the light emission command signal generated from the current to control the driving of the semiconductor laser and given from the pulse width modulation / intensity modulation signal generation unit. A current driver for flowing the semiconductor laser as a forward current; the pulse width modulation / intensity modulation signal generator, the error amplifier, and the current driver are formed by a one-chip integrated circuit; Since the unit is provided in the optical / electrical negative feedback loop, the current driver is also integrated with the error amplifier and incorporated in the optical / electrical negative feedback loop. It is easy to achieve integration, and in particular, it is possible to use only one high-current driving location, which is advantageous in reducing power consumption. Large-scale integration is also facilitated, and a small current , It is possible to drive at high speed.

According to the second aspect of the present invention, in the semiconductor laser control device according to the first aspect, an external element for setting a current value of the pulse width modulation / intensity modulation signal generation section is provided, Since the current of the modulation / intensity modulation signal generation unit is a DC monitor current of the light receiving element, it is necessary to set the current not to be affected by the temperature change inside the integrated circuit. The monitor current can be stabilized so that a desired optical output can be obtained in accordance with the characteristics of the semiconductor laser and the light receiving element, and can be adapted to a wide range of monitor current.

According to the third aspect of the present invention, in the semiconductor laser control device according to the first aspect, an external element for setting a control speed of the optical / electrical negative feedback loop is provided. And the control speed can be freely set to a desired value.

According to the fourth aspect of the present invention, in the semiconductor laser control device according to the first aspect, the current driver is a high-speed voltage shifter in the error amplifier, and the differential circuit changes the voltage shift amount. Is included in the optical / electrical negative feedback loop, so that further high-speed operation can be easily achieved by voltage driving by the high-speed voltage shift section, and the potential can be easily set.

According to a fifth aspect of the present invention, in the semiconductor laser control device according to the first aspect, the pulse width modulation / intensity modulation signal generation section outputs the first light emission command signal and the second light emission command signal. Since a plurality of D / A conversion circuits are used in common, the number of elements required for configuring the semiconductor laser control device according to claim 1 is reduced, and further reduction in power consumption and integration are facilitated. can do.

According to a sixth aspect of the present invention, in the semiconductor laser control device of the first aspect, the offset setting section having an external element for setting an offset current for setting the optical output of the semiconductor laser to a desired minimum value is provided. So we have
Regarding the offset current for controlling the optical output of the semiconductor laser in real time in the optical / electrical negative feedback loop, a desired offset current can be easily set by the offset setting unit by using an external device.

According to the seventh aspect of the present invention, in the semiconductor laser control device according to the first aspect, the maximum current of the pulse width modulation / intensity modulation signal generation section and the offset current that minimizes the optical output of the semiconductor laser. Since the setting of the offset current is performed in conjunction with the setting of the maximum current of the pulse width modulation / intensity modulation signal generation unit by providing the interlock setting unit having an external element for setting Can be automatically set so that the offset current becomes constant without changing the value of.

According to an eighth aspect of the present invention, in the semiconductor laser control device according to the first aspect, an offset setting unit having an external element for setting an offset current for setting the optical output of the semiconductor laser to a desired minimum value; , Pulse width modulation
Since there is provided an interlock setting unit having an external element for setting the maximum current of the intensity modulation signal generation unit and the offset current in an interlocked manner, the value of the external element is changed in the same manner as in the seventh aspect of the present invention. Even if it is not necessary, the offset current can be automatically set so as to be constant, and desired characteristics can be freely provided by using the offset setting unit.

According to a ninth aspect of the present invention, in the semiconductor laser control device according to the first aspect, the semiconductor laser control device further includes a start-up unit that allows the operation to start when the power supply voltage reaches a predetermined potential when the power is turned on. Since the start of the operation is allowed after the power supply voltage reaches a predetermined potential under the control of the section, the accuracy of the initialization of the integrated circuit can be improved, and the semiconductor laser can be protected at the time of rising.

According to the tenth aspect, the first aspect is provided.
In the semiconductor laser control device described in the above, the pulse width modulation / intensity modulation signal generation unit for flowing the absolute current determined by the light receiving element is the same as the number of switch transistors passing through the base current of the reference current with respect to the reference current. Since the base current compensating unit for compensating the base current is provided, by adding to the reference current by the number of switch transistors passing through the base current of the reference current, generation of an error current due to the base current and The characteristic change can be suppressed, and the current of the pulse width modulation / intensity modulation signal generation unit can be improved in accuracy.

According to the eleventh aspect, according to the first aspect,
In the semiconductor laser control device described in the above, the pulse width modulation
The pulse width modulation / intensity modulation signal generator, which has an external element for setting the current value of the intensity modulation signal generator and flows an absolute current determined by the light receiving element, generates a reference current with respect to a reference current. Since a base current compensator for compensating the base current by the number of switch transistors passing through the base current is provided, a desired optical output can be obtained in accordance with the characteristics of the semiconductor laser and the light receiving element by adjusting an external element. In addition to being able to stabilize the monitor current so that it can handle a wide range of monitor currents, it can also suppress the generation of error currents and characteristic changes due to the base current, and generate pulse width modulation and intensity modulation signals. The current of the section can be made highly accurate.

According to the twelfth aspect, according to the first aspect,
In the semiconductor laser control device described in the above, the pulse width modulation
Since there are a plurality of intensity modulation signal generators, it is possible to cope with a wide range of monitor currents, and it is possible to cope with differences in specifications of semiconductor lasers and light receiving elements.

According to the thirteenth aspect, according to the first aspect,
In the semiconductor laser control device described in the above, the pulse width modulation
An external control voltage input terminal that varies the maximum current of the intensity modulation signal generator is provided. Correction and fine adjustment of the light amount can be performed.

According to the fourteenth aspect of the present invention, the first aspect
The semiconductor laser control device according to the third aspect is provided with a start-up unit that allows the operation to start when the light emission command current corresponding to the light emission command signal reaches a predetermined current when the power is turned on. In addition, the initialization of the integrated circuit can be performed with higher accuracy, and the semiconductor laser can be protected at the time of startup.

According to the fifteenth aspect, according to the first aspect,
3. In the semiconductor laser control device according to 3, the addition current setting section for setting the drive current corresponding to the emission command signal, the maximum current by the pulse width modulation / intensity modulation signal generation section and the maximum current by the addition current setting section are linked. In the invention according to the thirteenth aspect, when the shading correction is performed dynamically, since the maximum current by the addition current setting unit is also interlocked, the optical output waveform can be approximated to an ideal square wave. .

According to the sixteenth aspect of the present invention, the first aspect
3. In the semiconductor laser control device according to 3, the start-up unit that permits the operation to start when the light-emitting command current corresponding to the light-emitting command signal reaches a predetermined current when the power is turned on, and an addition for setting the drive current corresponding to the light-emitting command signal. The invention according to claim 14, further comprising a current setting unit and an interlocking unit that interlocks the maximum current by the pulse width modulation / intensity modulation signal generation unit with the maximum current by the addition current setting unit. At the time of correction, the maximum current by the addition current setting unit is also linked, so that the optical output waveform can be approximated to an ideal square wave.

According to the seventeenth aspect, according to the first aspect,
3. In the semiconductor laser control device according to 3, the first start-up unit that allows the operation to start when the power supply voltage reaches a predetermined potential when the power is turned on, and the light emission command current corresponding to the light emission command signal becomes a predetermined current when the power is turned on. Since there is provided a second start-up unit which allows the operation to start when the time has been reached, in the invention according to the thirteenth aspect, similarly to the inventions according to the ninth and fourteenth aspects, the accuracy of the initialization of the integrated circuit is improved. And protection of the semiconductor laser at the time of rising can be achieved.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram illustrating a configuration example of an error amplification unit and a voltage shift unit.

FIG. 3 is a circuit diagram illustrating a configuration example of a power supply unit.

FIG. 4 is a circuit diagram showing a configuration example of a start-up unit.

FIG. 5 is a circuit diagram illustrating a configuration example of an oscillation circuit.

FIG. 6 is a circuit diagram illustrating a configuration example of a latch circuit.

FIG. 7 is a circuit diagram illustrating a configuration example of a last-stage latch circuit;

FIG. 8 is a time chart showing waveforms of respective parts.

FIG. 9 is a circuit diagram illustrating a configuration example of a differential quantum efficiency detection unit.

FIG. 10 is a circuit diagram illustrating a configuration example of a light emission command signal setting unit.

FIG. 11 is a circuit diagram illustrating a configuration example of a first light emission command signal generation unit.

FIG. 12 is a circuit diagram illustrating a configuration example of a second light emission command signal generation unit.

FIG. 13 is a characteristic diagram illustrating an example of light output control depending on the presence or absence of interlocking.

FIG. 14 is a circuit diagram showing a modification of the light emission command signal generator.

FIG. 15 is a circuit diagram showing an _IDA2 addition method by a conventional current driver.

FIG. 16 is a characteristic diagram showing an example of optical output control _depending on the presence or absence of P _S accompanying I _DA2 .

FIG. 17 is a block diagram showing a configuration example for a pulse width intensity mixing system.

FIG. 18 is a schematic diagram showing the relationship between the light output of the pulse width intensity mixing method and the dot image.

FIG. 19 is a time chart showing the waveform generation method.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 Driven semiconductor laser 2 Light receiving element 3 Optical / electrical negative feedback loop 20 Integrated circuit 21, 22 Pulse width modulation / intensity modulation signal generation unit 23 Error amplification unit 24 Current drive unit 25 High-speed voltage shift unit 34 Addition current setting unit 35 Startup part 35a first startup portion 35b second startup unit 42 differential circuit 73 the base current compensation unit 82, 83 offset setting unit 91 pulse width modulation and intensity modulation signal generator R _25, R _41, R ₅₁ external elements

Claims (17)

[Claims] 1. A pulse width modulation / intensity modulation signal generator for generating a light emission command signal for simultaneously performing pulse width modulation and intensity modulation on the input data based on the input data; a semiconductor laser; An optical / electrical negative feedback loop is formed together with a light receiving element that monitors the light output of the laser to provide a light receiving signal proportional to the light output of the semiconductor laser obtained from the light receiving element and the pulse width modulation / intensity modulation signal generation unit. An error amplifying unit that controls a forward current of the semiconductor laser so that an emission command signal to be output is equal to the control signal of the semiconductor laser. And a driving current corresponding to a light emission command signal generated from the pulse width modulation / intensity modulation signal generation unit and applied to the semiconductor laser. A pulse width modulation / intensity modulation signal generator, an error amplifier, and a current driver are formed by a one-chip integrated circuit. A semiconductor laser control device provided in an electric negative feedback loop. 2. The semiconductor laser control device according to claim 1, further comprising an external element for setting a current value of the pulse width modulation / intensity modulation signal generator. 3. The semiconductor laser control device according to claim 1, further comprising an external element for setting a control speed of the optical / electrical negative feedback loop. 4. The current driver is a high-speed voltage shifter in the error amplifier, and is provided in an optical / electrical negative feedback loop including a differential circuit for changing the amount of voltage shift. The semiconductor laser control device according to claim 1. 5. A pulse width modulation / intensity modulation signal generation unit,
2. The semiconductor laser control device according to claim 1, wherein a plurality of D / A conversion circuits for outputting the first light emission command signal and the second light emission command signal are shared. 6. The semiconductor laser control device according to claim 1, further comprising: an offset setting unit having an external element for setting an offset current for minimizing an optical output of the semiconductor laser to a desired minimum value. 7. An interlock setting unit having an external element for setting a maximum current of the pulse width modulation / intensity modulation signal generation unit and an offset current for minimizing an optical output of the semiconductor laser in an interlocking manner. 2. The semiconductor laser control device according to claim 1, wherein: 8. An offset setting unit having an external element for setting an offset current for minimizing an optical output of a semiconductor laser to a desired minimum value, and setting a maximum current of a light emission command signal generation unit and the offset current in conjunction with each other. 2. The semiconductor laser control device according to claim 1, further comprising: an interlocking setting unit having an external element. 9. The semiconductor laser control device according to claim 1, further comprising a start-up unit that allows the operation to start when the power supply voltage reaches a predetermined potential when the power is turned on. 10. A light emission command signal generating unit for flowing an absolute current determined by a light receiving element, wherein a base current for compensating for a base current by the number of switch transistors passing through the base current of the reference current is provided. The semiconductor laser control device according to claim 1, further comprising a compensator. 11. A light-emitting command signal generating unit having an external element for setting a current value of a pulse width modulation / intensity modulation signal generating unit and flowing an absolute current determined by a light-receiving element is provided for a reference current. 2. The semiconductor laser control device according to claim 1, further comprising a base current compensator for compensating the base current by the number of switch transistors passing through the base current of the reference current. 12. The semiconductor laser control device according to claim 1, wherein a plurality of pulse width modulation / intensity modulation signal generation units are provided. 13. The semiconductor laser control device according to claim 1, further comprising an input terminal for an external control voltage for varying a maximum current of the pulse width modulation / intensity modulation signal generation unit. 14. The semiconductor laser control device according to claim 13, further comprising a start-up unit that allows the operation to start when a light emission command current corresponding to the light emission command signal reaches a predetermined current when the power is turned on. 15. An addition current setting section for setting a drive current corresponding to a light emission command signal, and an interlocking section for linking a maximum current by the pulse width modulation / intensity modulation signal generation section with a maximum current by the addition current setting section. 14. The semiconductor laser control device according to claim 13, comprising: 16. A start-up unit for permitting operation to start when a light-emitting command current corresponding to a light-emitting command signal reaches a predetermined current when power is turned on, and an addition current setting unit for setting a drive current corresponding to the light-emitting command signal. 14. The semiconductor laser control device according to claim 13, further comprising an interlocking unit that interlocks the maximum current by the pulse width modulation / intensity modulation signal generation unit and the maximum current by the addition current setting unit. 17. A first start-up unit for permitting operation to start when a power supply voltage reaches a predetermined potential when the power is turned on, and when a light emission command current corresponding to a light emission command signal reaches a predetermined current when the power is turned on. 14. A second start-up unit for allowing operation to start.
14. The semiconductor laser control device according to claim 1.