JPH09266341A - Method and device for controlling semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optimized ideal light output waveform in the integrated circuit of one chip integrated by a bipolar transistor by resetting the optimum current adding value by detecting the change of the semiconductor laser differential quantum efficiency due to the lapse of time when initializing. SOLUTION: A semiconductor laser controller 13 is provided by integrating a pulse width generator, data modifier 11, semiconductor laser controller and a driving part 12 as an integrated circuit 20 of one chip, and a part of the circuit is made into one chip by a bipolar transistor. A block for detecting the differential quantum efficiency of the semiconductor laser 1 and setting a voltage shift quantity is composed of a timing generator 31, a differential quantum efficiency detecting part 32, memory part 33 and an adding current setting part 34. Thus, the optimized ideal light output waveform is always obtained.

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 method and apparatus for 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 A semiconductor laser is extremely small in size and can be directly modulated at a high speed by a driving current, so that it has been widely used in recent years as a light source for a laser printer or the like.

However, the relationship between the driving current of the semiconductor laser and the light output changes remarkably with temperature, which is a problem when the light intensity of the semiconductor laser is set to a desired value. In order to solve this problem and utilize the advantages of semiconductor lasers, various APCs (Automatic Power C
ontrol) circuit is proposed.

This APC circuit is roughly classified into the following three types. The light 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 the signal proportional to the light receiving current, which is proportional to the optical output of the semiconductor laser generated in the light receiving element, and the light emission level command signal become equal. A method of controlling the optical output of the semiconductor laser to a desired value by. The light output of the semiconductor laser is monitored by the light receiving element within the power setting period, and the signal proportional to the light receiving current (proportional to the light output of the semiconductor laser) generated in the light receiving element becomes equal to the light emission level command signal. As described above, by controlling the forward current of the semiconductor laser and holding the value in the forward direction of the semiconductor laser set during the power setting period outside the power setting period, the optical output of the semiconductor laser is controlled to a desired value. At the same time, outside the power setting period, information is added to 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 according to 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 the value.

In order to set the optical output of the semiconductor laser to a desired value, the method of is desirable. However, there is a limit to the control speed due to the limit of the operating speed of the light receiving element and the operating speed of the amplifying 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 taken into consideration as a measure of the control speed, 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 ; optical output of semiconductor laser P ₀ ; set light intensity of semiconductor laser t; approximated by time.

For many purposes of use of a semiconductor laser, the total amount of light (integrated value of light output ∫P) from immediately after the light output of the semiconductor laser is changed until a set time τ ₀ elapses.
_out · dt) is required to be a predetermined value, and ∫P _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 set, which is extremely difficult.

The method (2) is widely used because the semiconductor laser can be modulated at a high speed without causing the above problems due to the method (2). However, according to this method, since the light output of the semiconductor laser is not always controlled, the light quantity of the semiconductor laser easily changes due to disturbance or the like. As the disturbance, for example,
There is a droop characteristic of the semiconductor laser, and the light amount of the semiconductor laser easily causes an error of about several percent due to this droop characteristic. As an attempt to suppress the droop characteristic of the semiconductor laser, there has been proposed a method of compensating the frequency characteristic of the semiconductor laser drive current with the thermal time constant of the semiconductor laser, but the thermal time constant of the semiconductor laser is different for each semiconductor laser. However, there is a problem in that there are individual variations in the characteristics, and the characteristics vary depending on the surrounding environment of the semiconductor laser.

An improved method in consideration of such a point is proposed in, for example, Japanese Patent Laid-Open No. 205086/1990. According to the publication, as shown in FIG. 9, 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 monitored so that the output and the light emission level command signal (DATA) become equal. The optical / electrical negative feedback loop 3 for controlling the forward current and the current driver 4 for converting the emission level command signal (DATA) into the forward current of the semiconductor laser 1 are provided. Control current and current driver 4
There is disclosed a method of controlling the optical output of the semiconductor laser 1 by the current of the sum (or difference) of the drive currents generated by. In the illustrated example, the optical / electrical negative feedback loop 3 is composed of a semiconductor laser 1, a light receiving element 2, a constant current source 5 which is I _DA1, and an inverting amplifier 6, and the output of the inverting amplifier 6 causes a semiconductor together with a resistor R _e. It is configured to drive and control a drive transistor 7 connected in series to the laser 1. In addition, the current driver 4 has a constant current source 8 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
)} Is approximated. If P _S ≈P ₀ , the light output of the semiconductor laser instantly becomes equal to P ₀ , so the value of f ₀ may be smaller than in the case of only the optical / electrical negative feedback loop 3. While FIG. 10A shows how the optical output changes when only the optical / electrical negative feedback loop 3 is used, FIG. 10B shows the case where the constant current component I _DA2 by the current driver 4 is added. The change of the optical output of is shown. Realistically, f ₀ = 40 MH
It suffices that the frequency is z, and the crossover frequency of this level can be easily realized.

Next, taking the laser printer as an example, the background of the one-dot multi-valued technique will be described. The laser printer was originally developed as a non-impact printer that replaces the line printer, but due to the high speed and high resolution of the laser printer, its application as an image printer was considered from an early stage, and various recording methods based on the dither method were put into practical use. Has been converted. Also, due to the rapid progress of semiconductor technology in recent years, the amount of information that can be processed has increased rapidly, and in the laser printer, the one-dot multi-valued technology has been put into practical use, and while firmly solidifying its position as an image printer. is there. However, the current multi-valued level has an output level equivalent to 8 bits in a high-end machine, but is suppressed to a numerical value at most in a low-end machine. This is due to the large amount of information, which is mainly due to the fact that the circuit size of the semiconductor laser control modulator for realizing the one-dot multi-value output is large and expensive.

Currently, as a semiconductor laser control modulation method for performing one-dot multi-value output, A. Light intensity modulation method B. Pulse width modulation method C. A pulse width intensity mixed modulation method has been proposed.

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

B. Pulse width modulation method (PWM = Pulse
Width Modulation) Although the light output level is binary, it is a method of recording by changing the light emission time (that is, pulse width), so the intermediate exposure area is less utilized than the PM method, and By combining adjacent dots, it is possible to further reduce the intermediate exposure area (requirement for stability of the printing process is reduced). However, when the pulse width is set to 8 bits and the adjacent dot combination is realized, the structure of the semiconductor laser control modulator becomes complicated.

C. Pulse width intensity mixed modulation method (PWM +
PM method) The PM method has a strict requirement for stabilization of the printing process, and the PWM method has a problem that the semiconductor laser control modulator is complicated. Therefore, the PM method and the PWM method are combined. , For example, JP-A-6-3
It is disclosed in Japanese Patent No. 47852.

This modulation system is basically a binary recording system, and is based on a PWM system which is stable with respect to the printing process, and a transition system between the pulses is complemented by a PM system. This modulation method reduces the number of required pulse widths and power values when combined to achieve the same number of gradations, compared to individual modulation methods. In addition to being stable to the printing process and suitable for integration, it is possible to achieve downsizing and cost reduction.

In order to realize such a modulation method, the semiconductor laser control device basically includes a pulse width generation section and a data modulation section 11 for inputting image data and a pixel clock as shown in FIG. The pulse width generation section and the data modulation section 11 are provided so as to output DATA which is a light emission level command signal to the semiconductor laser control section and the semiconductor laser drive section 12 having the circuit configuration illustrated in FIG. . That is, according to the input image data, the pulse width generation section and the data modulation section 11 set the PWM method as the basic tone, and the transition section is complemented by the PM method. Figure 1 shows a basic conceptual diagram of the optical output waveform of the semiconductor laser.
It is shown in FIG. FIG. 12 schematically shows an optical output waveform of the semiconductor laser when outputting a total of 18 gradations of a pulse width of 3 values and a power of 6 values.

Since this modulation system is basically a PWM system as shown in the figure, it is necessary for the power 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. 13, PWM _OUT and PWM _OUT +
PM _OUT (PM _OUT is the minimum pulse width) or PWM _OU
Two pulses of _T and PM _OUT (PM _OUT is the minimum pulse width) may be generated. If all the bits are set to H level in the pulse of PWM _OUT and each bit is turned on / off according to the data in the pulse of PM _OUT , then FIG.
It is possible to obtain a light output waveform as shown in FIG. FIG.
The middle and upper rows show the right mode with right alignment, and the lower rows show the left mode with left alignment.

[0019]

In view of the technical background as described above, in order to obtain an ideally optimized ideal optical output waveform under high speed control, it is shown in FIG. 10 (b). P
It is important to set the _{S component} appropriately and make it closer to a square wave. In particular, this is important when attempting to realize more gradation modulation using the pulse width intensity mixing method described with reference to FIG.

Here, the general characteristics of the semiconductor laser are the operating current change characteristics with temperature as shown in FIG. 14 and the operating current change with time as shown in FIG. 15 (in particular, the differential quantum efficiency change). There is a characteristic. Among these, regarding the change characteristic of the operating current with temperature, even if the oscillation threshold current Ith of the semiconductor laser 1 changes with temperature, the change is caused by always operating the optical / electrical negative feedback loop 3 as shown in FIG. Since the control system follows, the control system always copes with the oscillation threshold current Ith as the forward current of the semiconductor laser 1.

However, as shown in the figure, an operating current change characteristic due to a change with time, in particular, a change in the differential quantum efficiency,
It shows larger change characteristics than the case with temperature. This change characteristic affects the P _{S component} shown in FIG.
There is an inconvenience that the optical output P _out to be obtained is too large to cause overshoot, or too small to cause undershoot to hinder high speed control.

That is, in the technical background as described above, no special measures are taken regarding the detection accuracy of the differential quantum efficiency of the semiconductor laser, and the detection accuracy is poor and the degree of freedom is small. Inadequate in approaching a simple rectangular wave.

[0023]

According to the first aspect of the present invention,
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; and a light 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 command signal given from the pulse width modulation / intensity modulation signal generating unit. An error amplifier for controlling a forward current of the semiconductor laser so that
A drive current corresponding to a light emission command signal generated from the pulse width modulation / intensity modulation signal generation unit is generated so as to control the driving of the semiconductor laser by a current that is the sum or difference of the control current of the electric negative feedback loop. A current drive unit for supplying a forward current to the semiconductor laser, a differential quantum efficiency detection unit for detecting the differential quantum efficiency of the semiconductor laser, a memory unit for storing the detection result of the differential quantum efficiency detection unit, and this memory unit. A summing current setting section for setting a current corresponding to the light emission command signal based on the detection result of the differential quantum efficiency detection section stored in, and a timing generation section as a one-chip integrated circuit integrated by bipolar transistors, At the time of initialization, the timing generation unit generates a timing signal that is sufficiently slower than the control speed of the error amplification unit. The differential quantum efficiency of the semiconductor laser is detected by the differential quantum efficiency detection unit based on a signal, the detection result at each timing is stored in the memory unit, and the light emission command signal is responded to according to the detection result stored in the memory unit. The current to be set is set.

According to a fifth aspect of the present invention, 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, and a semiconductor. A laser and a light receiving element for monitoring the light output of this semiconductor laser, together with 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 and the pulse width modulation An error amplification unit that controls the forward current of the semiconductor laser so that the light emission command signal given from the intensity modulation signal generation unit becomes equal to the sum or difference current of the control current of the optical / electrical negative feedback loop. A driving current corresponding to a light emission command signal generated to control the driving of the semiconductor laser and given from the pulse width modulation / intensity modulation signal generation unit is supplied to the semiconductor. A current drive unit that supplies a forward current to the laser, a differential quantum efficiency detection unit that detects the differential quantum efficiency of the semiconductor laser, and a timing generation that generates a timing signal that controls the detection operation of the differential quantum efficiency detection unit at initialization. Section, a memory section for storing the detection result at each timing of the differential quantum efficiency detection section, and a current corresponding to the light emission command signal is set by the detection result of the differential quantum efficiency detection section stored in this memory section. Integrated current setting unit and bipolar transistor integrated 1
It is provided as an integrated circuit of a chip.

Therefore, according to the first and fifth aspects of the present invention, the one-chip integrated circuit integrated with the bipolar transistor, which is preferable in terms of power saving and size reduction, is accompanied by a change with time. The change in the differential quantum efficiency of the semiconductor laser is detected at the time of initialization, such as when the power is turned on or when reset is released, and the optimal current addition value is set again to maximize the amount of high-speed control by the control unit that is an optical / electrical negative feedback loop. The optical output waveform of the semiconductor laser can be made closer to an ideal square wave without overshoot or undershoot, and an optimized ideal optical output waveform can be obtained at all times.

According to a sixth aspect of the present invention, in the fifth aspect of the present invention, the current drive section is a voltage shift section in the error amplification section, and includes an opto-electrical circuit including a differential circuit that changes the voltage shift amount. Provided in the negative feedback loop, the addition current setting unit, when the current corresponding to the light emission command signal is maximum, the optical output of the semiconductor laser becomes a desired maximum value, when the current corresponding to the light emission command signal is minimum. The current of the differential circuit is set so that the optical output of the semiconductor laser has a desired minimum value, and at the time of initialization, the optical output of the semiconductor laser is set to a desired maximum value at a certain timing T0. The optical output of the semiconductor laser is set to a desired minimum value at a timing T1 after a certain time has elapsed from the timing T1 and a certain constant from the timing T1. Wherein by operating the differential quantum efficiency detection unit and the addition current setting unit is to set the current between the timing T2 has elapsed between.

Therefore, by detecting the maximum value of the desired high-speed voltage shift amount, it is possible to provide one means for making the optical output waveform close to an ideal square wave.

According to the second and seventh aspects of the invention, the timing generation section includes an external element, and the timing signal set by the external element is generated.
Therefore, for example, when the delay circuit is used, the control speed of the optical / electrical negative feedback loop can be set freely, and the optical output waveform that is not affected by the frequency characteristics of the semiconductor laser-light receiving element can be obtained. This is convenient for optimizing the initialization time of the integrated circuit.

In the invention according to claim 3 or claim 8, the timing generation section includes an oscillation circuit and generates a plurality of timing signals based on the oscillation output of the oscillation circuit. Therefore, by using the oscillation circuit in the timing generation unit, even if the number of timings to be generated is large, the timings can be freely set by providing only one external capacitor. Furthermore, a circuit for compensating the frequency characteristic can be eliminated by simply changing the capacitance of the capacitor.

In the invention according to claim 4 or claim 9, the timing generation section includes an oscillation circuit and a multi-stage latch circuit,
Each latch circuit generates a timing signal based on the oscillation output of the oscillation circuit. Therefore, by combining the oscillation circuit with the latch circuit instead of the flip-flop, it is possible to obtain a circuit configuration in which the number of elements is reduced.

[0031]

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 method as described above, or the light / light
The electric negative feedback loop + addition current value control method is followed, and the same parts as those shown in FIGS. 9 to 15 are denoted by the same reference numerals.

That is, the semiconductor laser control device 13 according to the present embodiment is roughly as shown in FIG.
It comprises a pulse width generator and data modulator 11, a semiconductor laser controller and a semiconductor laser driver 12. Here, the semiconductor laser control section and the semiconductor laser drive section 12 are mainly composed of an optical / electrical negative feedback loop 3 and a current drive section 4 as shown in FIG. As a result, the data already PWM-modulated by the pulse width generation unit and the data modulation unit 11 is input to the constant current sources 5 and 8, and the current value I _DA1 of the constant current source 5 is the inverting amplifier 6, the semiconductor laser 1, and the received light. The optical / electrical negative feedback loop 3 is formed via the element 2, and the current value I _DA2 of the constant current source 8 becomes the forward current of the semiconductor laser 1 and is converted into the optical output of the semiconductor laser 1 at high speed, thereby achieving high speed. In addition, the semiconductor laser 1 can be controlled and driven. In this case, the current I _DA2 generated by the constant current source 8 functioning as the current driver 4 and thus the optical output P _S
By setting the value of 1 to a desired value, the optical output of the semiconductor laser 1 can be PWM- and PM-modulated at high speed as described above.

FIG. 1 shows a more detailed configuration example of the semiconductor laser control device 13 in the present embodiment. First, in the present embodiment, the pulse width generation unit and the data modulation unit 11 that generate a plurality of pulses by converting the input data into the pulse width modulation data and the intensity modulation data, and the semiconductor laser control unit and the drive unit 12, Most of the elements except some of the constituent elements are integrated and configured as a one-chip integrated circuit 20. More specifically, as will be described later with respect to a part of the circuit configuration, it is integrated into one chip by bipolar transistors. Here, the pulse width generation unit and the data modulation unit 11 will not be described in detail, but for example, a pulse generation unit having a PLL configuration for generating a plurality of pulses with different timings, and the input image data as pulse width modulation data. And a intensity conversion data and a data conversion unit including a logical description, and a pulse width modulation unit that selects a pulse from the output of the pulse generation unit according to the pulse width modulation data obtained from the data conversion unit. But
The circuit configuration is based on bipolar transistors that execute these logical descriptions.

The semiconductor laser control section and the drive section 12 side will be described below. 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 2.
2, an error amplifier 23 (corresponding to the inverting amplifier 6), a current driver 24, the semiconductor laser 1, and the light receiving element 2. As the operation, the current generated by the light emission command signal generator 22 according to 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 amount is compared. Is converted into a forward current of the semiconductor laser 1 via the error amplifier 23 and the current driver 24 to form the optical / electrical negative feedback loop 3. Here, in general, there are element variations in the differential quantum efficiency of the semiconductor laser 1 and the light-to-electricity conversion light receiving sensitivity of the light receiving element 2, so it is necessary to set the current value according to each characteristic. With respect to such element variations, the light emission command signal setting unit 21 sets the current value I _DA1 by an external current setting signal so that the semiconductor laser 1 has a desired optical output, that is, the light receiving element in DC operation. By setting the monitor current value of 2, it becomes possible to absorb individual differences and set the semiconductor laser 1 to always have a desired optical output.

The current drive section 24 is constructed as a voltage shift section 25 which instantaneously shifts the output of the error amplifier 23 by a desired potential by a differential switch configuration, for example. The voltage shift by the voltage shift unit 25 instantly becomes the forward current of the semiconductor laser 1, and the optical output of the semiconductor laser 1 can be modulated at high speed. In particular, by providing a voltage shift unit 25 functioning as the current driver 24 in the control system of the optical / electrical negative feedback loop 3 and providing the same output unit as the optical / electrical negative feedback loop 3 side, In configuring, the number of elements and the power consumption can be reduced.

FIG. 2 shows the error amplifier 23 and the voltage shift unit 2.
An example of a circuit configuration using the bipolar transistor of No. 5 is shown. First, at the PD terminal of the light emission command signal generation unit 22, the data input by the D / A conversion unit in the light emission command signal generation unit 22 is converted into the current I _DA1 , and the light of the semiconductor laser 1 is emitted from the light receiving element 2. The monitor current I _PD flowing in proportion to the output is compared, and the result is compared to the light emission command signal generation unit 22.
Detect at the base of the inside transistor Q ₁ . 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. Between the differential amplifier 41 and the LD terminal, the transistors Q ₄ , Q ₅ and the resistor R
_The voltage shift unit 25 is configured to instantaneously shift the voltage of the output by a desired potential by the differential switch 42 configured by _{2 and the} like, which serves as a differential circuit. 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 drive transistor 7 that finally drives the semiconductor laser 1 and the resistor _Re are externally attached to the integrated circuit 20. the R _e, it is necessary to flow a few tens to several hundreds mA current of about to drive the semiconductor laser 1, the case of the structure described in this embodiment, the semiconductor laser control unit and a semiconductor laser driving unit 12 A few mA is enough for the current in the output section connected to the drive section, so the power consumption is reduced,
Easy integration. In the circuit shown in FIG. 2, it is the resistance R that determines the voltage shift amount of the current driver 24.
₂ and R ₃ , the transistor Q _9, etc., the differential quantum efficiency of the semiconductor laser 1 varies as described above, and the efficiency deteriorates over time. By detecting and setting the voltage shift amount, the above-described FIG.
It is possible to obtain an optical output in which the optical output P _S as shown in FIG. Further, in the circuit shown in FIG. 2, the differential amplifier 41 composed of the transistors Q ₂ , Q _{3 and the} like constitutes its output as a voltage drop in the resistor R ₄ from the power supply voltage Vcc. Since the negative feedback loop 3 controls the optical output of the semiconductor laser 1 in real time,
It also controls power supply voltage fluctuations. In addition, the light receiving element 2
In the process of inputting to the differential amplifier 41 the result of detection at the PD terminal (base potential of the transistor Q _{4 in} the light emission command signal generation unit 22) via the transistors Q ₁₁ , Q ₁₂ , and the resistor R _4. This differential amplifier 41 is being fed back.
The voltage gain of is determined by the resistance values of resistors R ₅ and R ₆ ,
By reducing the gain, the crossover frequency of the differential amplifier 41 is increased and the 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 initializing operation only at a predetermined initializing time such as when the power is turned on or at the time of resetting (when the optical output of the semiconductor laser 1 is turned off), and the current value of the addition current setting unit 34 is held during the normal operation.

A startup unit 35 is connected to the timing generation unit 31. 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 still reaches a predetermined value when the power is turned on, and performs the timing generation. The section 31 plays a role of generating a necessary initialization start signal. A certain set potential set in the start-up unit 35 is set to a potential as close as possible to a predetermined power supply voltage. 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. Specifically, the output of the error amplifier 23 is forcibly set to L level by forcibly setting the potential of the terminal of the light receiving element 2 to H level, and the forward current of the semiconductor laser 1 is suppressed so as not to flow. This protects the semiconductor laser 1. At the same time, as described later, by forcibly setting the potential of the TDSTART terminal to the H level, the oscillation circuit (described later) in the timing generator 31 is suppressed from forcibly oscillating. When the power supply voltage (here, Vcc) becomes equal to or higher than a certain set potential, the protection of the semiconductor laser 1 is released to bring the semiconductor laser 1 into a normal operation state, and the oscillation suppression of the oscillation circuit in the timing generator 31 is released. Is used as an oscillation start signal. At the same time, the VPTDSTART terminal potential for generating the current source of the timing generator 31 is output.

The timing generator 31 can be constructed by using, for example, a delay circuit, but in the present embodiment, it is constructed by an oscillation circuit 36, a bias circuit (not shown), and a latch circuit 37. Has been done. 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 detecting section 32 is, for example,
It comprises a sample hold circuit 38 for detecting the peak value in the error output of the error amplifier 23, and a comparator 39 for comparing the output value of the sample hold circuit 38 with a predetermined value.

The memory section 33 has a function of holding the comparison result of the comparator 39 in synchronization with the timings T1 to T5 generated by the timing generation section 31.
The addition current setting unit 34 includes, for example, a 5-bit D / A
It is constituted by a converter 40.

Next, the structure, operation and the like of each of these parts will be described. First, FIG. 3 shows a circuit configuration example of the oscillation circuit 36 using bipolar transistors. Further, FIG. 5 shows a schematic operation at the time of initialization. Transistor Q ₂₂
The collector potential V _Q22C of the transistor Q ₂₂ is expressed as the oscillating operation in FIG. 4, and the collector current of the transistor Q _{22 is} turned on and off by the differential switch 46 composed of the transistors Q ₂₄ and Q ₂₅ , and the collector of the transistor Q ₂₂ is When the current is larger than the collector current of the transistor Q ₂₁ when it is on, the collector potential V _Q22C of the transistor Q _{22 oscillates} as each current repeatedly charges and discharges the capacitor C ₁ .

First, the timing 0 shown in FIG. 4, that is,
From the time the power is turned on until the oscillation start timing signal TS is sent from the startup unit 35, TDST
The potential of the ART terminal is forcibly H level (almost the same potential as Vcc), and the VPTDSTART terminal is 0V, so V
The collector current of the transistor Q ₂₃ generated from the PTDSTART terminal is 0, and the transistor Q _{25 of} the differential switch 46 is also at the L level, but the collector current of the transistor Q ₂₃ is 0, so the collector current of the transistor Q ₂₂ is 0. Is also 0. After that, the oscillation start timing signal T
After passing S, the collector current of the transistor Q ₂₂ begins to flow, and the transistor Q _{25 of the} differential switch 46 becomes L.
Since it is at the level, the collector current of the transistor Q _{23 is} the current mirror circuit 47 formed by the transistors Q ₂₂ and Q _26.
And becomes the collector current of the transistor Q ₂₂ . This timing TS, since the current of the power supply unit (not shown) is zero, the collector potential V _Q22C transistor Q ₂₂ in the case the collector current of the transistor Q ₂₂ is greater than the collector current of the transistor Q _21, i.e., TDSTAR
The T terminal potential gradually decreases. Then, at the moment when the base potential of the transistor Q ₂₄ becomes equal to or lower than the base potential of the transistor Q ₂₅ , the differential switch 46 operates, turning on the transistor Q _{24 and} turning on the transistor Q _24.
The collector current of ₂₆ , and hence the collector current of the transistor Q ₂₂ , is turned off, and the base potential of the transistor Q ₂₅ rises by the potential determined by the collector current of the transistor Q ₂₄ and the resistor R ₁₁ . This moment is timing T0.

After the timing T0, the collector current of the transistor Q ₂₂ is turned off, so that the transistor Q ₂₂ is turned off.
₂₂ collector potential V _Q22C , that is, the TDSTART terminal potential is
Gradually rise. Then, at the moment when the base potential of the transistor Q ₂₄ becomes equal to or higher than the base potential of the transistor Q ₂₅ , the differential switch 46 is inverted, and the oscillating operation in which the collector current of the transistor Q ₂₂ is turned on is repeated. The amplitude of this oscillation is determined by the potential determined by the collector current of the transistor Q ₂₄ and the resistor R _11, and the cycle is determined by the collector current of the transistor Q ₂₁ , the collector current of the transistor Q ₂₂ , and the capacitance of the capacitor C _1. A desired timing signal can be obtained by appropriately determining the value of.

In such an operation, the transistor Q
_When the collector current of ₂₂ is just twice the collector current of transistor Q ₂₁ , the collector current of transistor Q ₂₁
(Collector current of transistor Q ₂₂ ) − (Collector current of transistor Q ₂₁ ) becomes equal, and the amount of charge per unit time charged and discharged in the capacitor C ₁ becomes equal. Therefore, as shown in FIG. What
The rising time and the falling time are triangular waves.

As a oscillating output of the oscillating circuit 36, a square wave is obtained at the base of the transistor Q ₂₅ , which is subjected to voltage shift, swing amount adjustment, and inversion processing, and then FIG.
An output waveform of the emitter potential V _QXE of the transistor Q _X shown therein is obtained.

Next, FIG. 4 shows a circuit configuration example of the latch circuit 48 which is one structural 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. However, FIG. Is shown.
In the illustrated example, a plurality of transistors and resistors are configured as constituent elements, and among these, the transistors Q ₃₁ to
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.

The base of the transistor Q ₃₃ is CLK, the base of the transistor Q ₃₆ is / CLK ("/" indicates inversion with respect to the signal), the base of the transistor Q ₃₁ is DATA 0, and the emitter of the transistor Q ₃₇ is output Q. When these relationships are expressed by a logical expression, Q = CLK.DATA0 + / CLK.Q.

Here, as described above, the transistor Q _X
The emitter potential V _QXE (see FIG. 5), that is, the base / CLK of the transistor Q ₃₆ is in the output holding state at the H level from the timing TS to the timing T0, and is composed of the transistors Q ₃₈ and Q _39. The current source 50 uses the VPTDSTART from the start-up unit 35 as the base potential, so that the current flows from the moment when the current becomes 0 and reaches the timing TS until the timing TS, so the output Q is at the H level until the timing T0. . Timing T
When it becomes 0, the output Q becomes L level for the first time, and after the timing T0, the base (input data) of the transistor Q _31.
Is at the L level, the output Q maintains the L level. This state is shown as a waveform of the emitter potential V _{Q3 7E} (timing signal T0) of the transistor Q ₃₇ in FIG.

In the next stage (not shown), CLK is inverted and input,
When the emitter potential V _Q37E of the transistor Q ₃₇ is DATA1, Q '= / _{CLK.multidot.DATA1} + _{CLK.multidot.Q} ', so that the timing signal T1 shown by _{V.sub.Q37 (1) E} in FIG. 5 can be obtained.

Thereafter, the timing signals T2 to T5 can be similarly obtained. "N" in V _{Q37 (n) E} in Fig. 5
Indicates the number of stages 1 to 5.

Further, in the final stage latch circuit for generating the timing signal T5, the collector current of the transistor (corresponding to the transistor Q ₃₁ in FIG. 4) whose base is the data input portion is oscillated by the oscillator circuit 36 or the like. By setting the base current of the transistor Q _{5 in} the inside, that is, the current for driving the oscillation circuit 36, a current flows from timing TS to timing T4, but at the moment of timing T4, the base current of transistor Q ₅ , and therefore It becomes possible to turn off the collector current.

That is, by oscillating only while the required timing signal is generated, and stopping the oscillation at the same time when the desired timing signal is generated, the oscillation operation of the oscillation circuit 36 causes noise and current fluctuations in other circuits. It has a circuit configuration that does not adversely affect. 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.

Further, generally, there is a frequency characteristic between the semiconductor laser 1 and the light receiving element 2, and this frequency characteristic is used for the operation of the above-mentioned control system (optical / electrical negative feedback loop 3) and the above-mentioned timing setting. There is no problem if the characteristics are not affected, but if the frequency characteristics are not good, if the above-mentioned timing is constant, the semiconductor laser 1 and the light receiving element 2 are not connected. It is necessary to add a circuit for compensating the frequency characteristic or set the above-mentioned timing 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, the schematic operation at the time of initialization controlled by these timing signals will be described with reference to the time chart of FIG. 5 and the circuit configuration example of the differential quantum efficiency detection unit 32 shown in FIG. First, the optical output of the semiconductor laser 1 is set to a desired maximum light emission state from the forced off state at the timing TS. It is assumed that this maximum light emission value has already been set in the light emission command current generation unit 22. Then, at timing T0, all the input data are set to 0, and the offset light emission state is maintained. After this state is maintained until timing T5, the normal operation state for receiving the original input data is set after timing T5. In order to operate the optical / electrical negative feedback loop 3, it is necessary to perform offset light emission in which the optical output of the semiconductor laser 1 is not turned off completely but slightly emitted. In reality, the optical output of the semiconductor laser 1 is , Is controlled by the optical / electrical negative feedback loop 3 between the set maximum emission and offset emission.

The optical output of the semiconductor laser 1 always detects the differential quantum efficiency by executing the sequence operation as shown in FIG. 5 at the time of initialization, that is, when the power is turned on or the reset is released. Set an appropriate added current value.

The difference between the maximum emission and the offset emission as shown in FIG. 5, that is, operating current Iop-oscillation threshold current Ith
Is the differential quantum efficiency, the sample hold circuit 38 in the differential quantum efficiency detection unit 32 detects this difference. As a rough operation, this difference is the resistance R as a voltage.
₇ (see FIG. 2), which is the emitter potential output of the transistor Q ₉ in the error amplifier 24 when the voltage shift section 25, which is the current drive section 24, is not operating. The emitter potential of the transistor Q ₉ is sampled and held, and the potential shift amount of the voltage shift unit 25, which was 0 at the timing T0, is gradually changed by the addition current setting unit 34, and the difference is calculated by the resistance of the voltage shift unit 25. The differential quantum efficiency is detected by setting the potential change of R ₁ .

More specifically, the emitter potential of the transistor Q ₉ , that is, the VCOMP terminal becomes the base potential of the transistor Q ₄₃ via the emitter follower 51 of the transistor Q ₄₂ . 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 transistor by constituted voltage follower 53 in the transistor _{Q 41, Q 46, Q 47} , Q 48 , etc. as the base potential and the same potential of Q _44. Current source 52 at timing T0
When the current is turned off, the change in the base potential of the transistor Q ₄₃ shows the change in the potential of the VCOMP terminal as it is, but the base potential of the transistor Q ₄₄ does not change as the capacitance of the capacitor C ₂ increases, and the transistor Q _{43 at} the timing T0. It is possible to sample and hold the base potential of ₄₃ , that is, the emitter potential of the transistor Q ₉ (see FIG. 2) at the time of maximum light emission. The lower part of FIG. 5 shows a schematic waveform sampled and held by these transistors Q ₄₃ and Q ₄₄ .

The base potentials of these sample-held transistors Q ₄₃ and Q ₄₄ are transferred to the transistors Q ₄₉ and Q _50.
Are input to the comparator 39 to compare the magnitudes thereof, and the comparison result is synchronized with the timing signals T1 to T5 in the memory unit 3
Hold at 3. Therefore, although not particularly shown in the configuration example, the memory unit 33 has only to have a function of holding the comparison output of the comparator 39 in synchronization with the timing signals T1 to T5. For example, the timing generation unit 31. In the comparison of the comparator 39, the base potential on the transistor Q ₄₃ side is the transistor Q _44.
It may be configured to output the L level when it is higher than the base potential on the side.

The addition current setting section 34 adds five switches composed of two stages of differential switches, a current mirror circuit for supplying a current to the current sources of these switch sections, and the output of each switch section. The current driver (voltage shift unit 2
5) and a current mirror circuit which is an output. Here, a 5-bit D / A converter 40 is basically constituted by five switch parts, and the current sources of these switch parts have a minimum bit current of I1 and a switch part of the next bit has a 2-bit value. * I1, and 4 * I1, 8 * I1, and 16 * I1 are set for each switch part of the higher bits. As a result, the maximum output current of the entire switch unit is 31 * I1, and at this time, the maximum current (maximum voltage) set in the current drive unit (voltage shift unit 25) is the above-mentioned (operating current Iop)-( The oscillation threshold current Ith) is set to be larger than the maximum value.

At timing T0, the optical output of the semiconductor laser 1 is changed from the maximum light emission state to the offset light emission state as shown in FIG. 5, and at the same time, the current of the most significant bit of the switch section is forcibly output. In this state, the maximum light emission state is offset and the current of the switch section of the most significant bit is forcibly output, causing a potential change in the terminal potential of the voltage shift section. Control is performed by the control system 3 so that the optical output of the semiconductor laser 1 is in the offset light emission state, so that it changes so as to compensate for the difference in these potential changes. Such a variation is detected by the differential quantum efficiency detection unit 32, its output is compared with the maximum light emission state, and the comparison result is stored in the memory unit 33.
To be stored. The memory unit 33 displays this result at the timing T
When the potential is larger than the potential of the maximum light emitting state, it is turned off, and when it is smaller, it is turned on. Here, the timings T1 to T0 need to be set to a time during which the control system of the optical / electrical negative feedback loop 3 sufficiently converges during this period.

Timing T0 also at timing T1
As in the case of, the upper 2nd bit is forcibly output,
The result is reset at timing T2. In the present embodiment, since the differential quantum efficiency is detected with the accuracy of D / A for 5 bits, the same is repeated for 5 bits.
The change in the base potential at this time is illustrated in the same manner as in the case of the base potential of the transistor Q ₄₄ shown in the lower portion of 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 the present embodiment, the differential quantum efficiency detection unit 3
2 and although the detection accuracy of the added current setting unit 34 and 5 bits, by raising the detection accuracy further increasing the number of bits, in the optical output waveform shown in FIG. 10 (b), P _S content of the light output amount of the desired The optical output becomes, and the control of the optical output by the control system, which is the optical / electrical negative feedback loop 3, is reduced, and the optical output waveform approaches a more ideal square wave.

Further, in the present embodiment, the current driver 24
In the example described above, the voltage shift unit 25 is interposed in the optical / electrical negative feedback loop 3. However, for example, as shown in FIG. The drive unit 24 may be provided. Further, as for the light emission command signal generation unit and the light emission command signal setting unit, as shown in FIG. 8, the light emission command signal generation unit 22a and the light emission command signal setting unit 21a dedicated to I _DA1 and the light emission command signal dedicated to I _DA2 are included. Generation unit 22b and light emission command signal setting unit 2
1b may be divided and comprised. In this case, the light emission command signal setting unit 21b serves as the addition current setting unit 34.

[0065]

According to the first and fifth aspects of the present invention, the pulse width modulation / intensity modulation signal generator, the error amplifier, and the current driver as well as the differential quantum efficiency detector for detecting the differential quantum efficiency of the semiconductor laser. A memory unit that stores the detection result of the differential quantum efficiency detection unit, and an addition current setting unit that sets a current corresponding to the light emission command signal based on the detection result of the differential quantum efficiency detection unit stored in the memory unit, Integrated timing generator with bipolar transistor 1
Provided as an integrated circuit of the chip, at the time of initialization, the timing generation unit generates a timing signal sufficiently slower than the control speed of the error amplification unit, and the differential quantum efficiency detection unit detects the differential quantum efficiency of the semiconductor laser based on the timing signal, The detection result at each timing is stored in the memory unit, and the current corresponding to the light emission command signal is set according to the detection result stored in the memory unit. Therefore, it is preferable for power saving and miniaturization. In a one-chip integrated circuit integrated with transistors, it is necessary to detect the change in the differential quantum efficiency of the semiconductor laser with the passage of time at the time of initialization such as when the power is turned on or when reset is released, and reset the optimum current addition value. This reduces the amount of high-speed control by the control unit that is an optical / electrical negative feedback loop as much as possible. Can, without overshoot or undershoot the optical output waveform of the semiconductor laser, close to the square wave of the ideal, always it is possible to obtain an optimized ideal optical output waveform.

According to a sixth aspect of the present invention, in the fifth aspect of the invention, the current drive section is a voltage shift section in the error amplification section, and an optical circuit including a differential circuit for changing the voltage shift amount is provided.・ Provided in the electric negative feedback loop,
The addition current setting unit sets the optical output of the semiconductor laser to a desired maximum value when the current corresponding to the light emission command signal is the maximum, and the optical output of the semiconductor laser is desired when the current corresponding to the light emission command signal is the minimum. It is assumed that the current of the differential circuit is set to be the minimum value of the above, and at the time of initialization, the optical output of the semiconductor laser is set to a desired maximum value at a certain timing T0 and a timing when a certain fixed time has elapsed from the above timing T0. The optical output of the semiconductor laser is set to a desired minimum value at T1, and the differential quantum efficiency detection unit and the addition current setting unit are operated between the timing T1 and a timing T2 when a certain fixed time has elapsed from the timing T1. Since the current is set, by detecting the maximum value of the desired high-speed voltage shift amount, the optical output waveform can be converted into an ideal square wave. It may provide one means capable close.

According to the inventions of claims 2 and 7,
Since the timing generation unit includes the external element and is configured to generate the timing signal set by the external element, for example, when the timing generation unit is configured by the delay circuit, the control speed of the optical / electrical negative feedback loop is increased. Can be set freely, and an optical output waveform that is not affected by the frequency characteristics of the semiconductor laser-light receiving element can be obtained, which is convenient for optimizing the initialization time of the integrated circuit.

According to the invention described in claims 3 and 8,
Since the timing generation unit includes the oscillation circuit and generates the plurality of timing signals based on the oscillation output of the oscillation circuit, it is possible to use the oscillation circuit in the timing generation unit to generate a large number of timings. However, the timing can be freely set by providing only one external capacitor, and further, only by changing the capacitance of the capacitor, a circuit for compensating the frequency characteristic can be eliminated.

According to the inventions of claims 4 and 9,
Since the timing generation unit includes an oscillation circuit and a multi-stage latch circuit, and each of the latch circuits generates a timing signal based on the oscillation output of the oscillation circuit, the timing circuit is not a flip-flop but a latch. By combining circuits, it is possible to form a circuit configuration in which the number of elements is reduced.

[Brief description of drawings]

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

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

FIG. 3 is a circuit diagram illustrating a configuration example of an oscillation circuit.

FIG. 4 is a circuit diagram illustrating a configuration example of a latch circuit.

FIG. 5 is a time chart showing the waveform of each part.

FIG. 6 is a circuit diagram showing a configuration example of a differential quantum efficiency detection unit.

FIG. 7 is a schematic block diagram showing a modified example.

FIG. 8 is a schematic block diagram showing another modified example.

FIG. 9 is a circuit diagram showing an I _DA2 addition method by a conventional current driver.

FIG. 10 is a characteristic diagram showing an example of optical output control _depending on the presence or absence of P _S associated with I _DA2 .

FIG. 11 is a block diagram showing a configuration example for a pulse width intensity mixing method.

FIG. 12 is a schematic diagram showing a relationship between a pulse width intensity mixing type optical output and a dot image.

FIG. 13 is a time chart showing the waveform generation method.

FIG. 14 is a characteristic diagram showing operating current change characteristics with temperature.

FIG. 15 is a characteristic diagram showing operating current change characteristics due to changes over time.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 semiconductor laser 2 light receiving element 3 optical / electrical negative feedback loop 23 error amplification section 24 current drive section 25 voltage shift section 31 timing generation section 32 differential quantum efficiency detection section 33 memory section 34 addition current setting section 36 oscillation circuit 37 latch circuit 42 Differential circuit

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[Procedure amendment]

[Submission date] June 17, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction contents]

However, as shown in the figure, an operating current change characteristic due to a change with time, in particular, a change in the differential quantum efficiency,
It shows larger change characteristics than the case with temperature. This change characteristic affects the P _{S component} shown in FIG.
Or cause the overshoot is too large for the light output P _out to be obtained, there is a disadvantage of the like or too small to interfere with the high-speed control.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0052

[Correction method] Change

[Correction contents]

Further, in the final stage latch circuit for generating the timing signal T5, the collector current of the transistor (corresponding to the transistor Q ₃₁ in FIG. 4) whose base is the data input portion is oscillated by the oscillator circuit 36 or the like. The base current of the transistor Q _{23 in} the inside, that is, the current for driving the oscillation circuit 36, causes the current to flow from the timing TS to the timing T 5, but at the moment of timing T 5 , the base current of the transistor Q ₂₃ . Therefore, it is possible to turn off the collector current.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0057

[Correction method] Change

[Correction contents]

The difference between the maximum emission and the offset emission as shown in FIG. 5, that is, operating current Iop-oscillation threshold current Ith
Is the differential quantum efficiency, the sample hold circuit 38 in the differential quantum efficiency detection unit 32 detects this difference. As a rough operation, this difference is the resistance R as a voltage.
₁ (see FIG. 2), which is the emitter potential output of the transistor Q ₁₂ in the error amplifier 24 when the voltage shift unit 25, which is the current driver 24, is not operating. The emitter potential of the transistor Q ₁₂ is sampled and held, and the potential shift amount of the voltage shift unit 25, which was 0 at the timing T0, is gradually changed by the addition current setting unit 34, and the difference is calculated by the resistance of the voltage shift unit 25. The differential quantum efficiency is detected by setting the potential change of R ₂ .

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0058

[Correction method] Change

[Correction contents]

More specifically, the emitter potential of the transistor Q ₁₂ , that is, the VCOMP terminal becomes the base potential of the transistor Q ₄₃ via the emitter follower 51 of the transistor Q ₄₂ . 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 transistor by constituted voltage follower 53 in the transistor _{Q 41, Q 46, Q 47} , Q 48 , etc. as the base potential and the same potential of Q _44. Current source 52 at timing T0
When the current is turned off, the change in the base potential of the transistor Q ₄₃ shows the change in the potential of the VCOMP terminal as it is, but the base potential of the transistor Q ₄₄ does not change as the capacitance of the capacitor C ₂ increases, and the transistor Q _{43 at} the timing T0. It is possible to sample and hold the base potential of ₄₃ , that is, the emitter potential of the transistor Q ₁₂ (see FIG. 2) at the time of maximum light emission. The lower part of FIG. 5 shows a schematic waveform sampled and held by these transistors Q ₄₃ and Q ₄₄ .

[Procedure Amendment 5]

[Document name to be amended] Drawing

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

FIG.

[Procedure correction 6]

[Document name to be amended] Drawing

[Correction target item name] Figure 2

[Correction method] Change

[Correction contents]

[Fig. 2]

[Procedure amendment 7]

[Document name to be amended] Drawing

[Correction target item name] Figure 3

[Correction method] Change

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[Figure 3]

[Procedure amendment 8]

[Document name to be amended] Drawing

[Correction target item name] Fig. 4

[Correction method] Change

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FIG. 4

[Procedure amendment 9]

[Document name to be amended] Drawing

[Correction target item name] Fig. 6

[Correction method] Change

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FIG. 6

[Procedure amendment 10]

[Document name to be amended] Drawing

[Name of item to be corrected] Figure 7

[Correction method] Change

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FIG. 7

[Procedure amendment 11]

[Document name to be amended] Drawing

[Correction target item name] Fig. 8

[Correction method] Change

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[Figure 8]

[Procedure amendment 12]

[Document name to be amended] Drawing

[Correction target item name] FIG.

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[Procedure amendment 13]

[Document name to be amended] Drawing

[Correction target item name] FIG.

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FIG.

Claims (9)

[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, and this semiconductor laser. From the light receiving element for monitoring the optical output of the semiconductor laser and the light receiving signal proportional to the optical output of the semiconductor laser obtained from the light receiving element by forming an optical / electrical negative feedback loop together with the pulse width modulation / intensity modulation signal generating section. The semiconductor laser is driven by a current that is the sum or difference of the error amplification unit that controls the forward current of the semiconductor laser so that the given emission command signal becomes equal, and the control current of the optical / electrical negative feedback loop. A forward current to the semiconductor laser, which is generated so as to be controlled, is supplied to the semiconductor laser with a drive current according to a light emission command signal given from the pulse width modulation / intensity modulation signal generation unit A current drive unit to flow, a differential quantum efficiency detection unit that detects the differential quantum efficiency of the semiconductor laser, a memory unit that stores the detection result of the differential quantum efficiency detection unit, and the differential quantum efficiency stored in this memory unit. The integrated current setting unit that sets the current corresponding to the light emission command signal according to the detection result of the detection unit, and the timing generation unit are provided as a one-chip integrated circuit integrated by bipolar transistors, and the timing generation unit is used at the time of initialization. A timing signal that is sufficiently slower than the control speed of the error amplification unit is generated, and the differential quantum efficiency of the semiconductor laser is detected by the differential quantum efficiency detection unit based on the timing signal,
A semiconductor laser control method, wherein a detection result at each timing is stored in the memory unit, and a current corresponding to a light emission command signal is set according to the detection result stored in the memory unit. 2. The timing generator includes an external element,
The semiconductor laser control method according to claim 1, wherein the timing signal set by the external element is generated. 3. The semiconductor laser control method according to claim 1, wherein the timing generation section includes an oscillation circuit, and generates a plurality of timing signals based on the oscillation output of the oscillation circuit. 4. The semiconductor device according to claim 1, wherein the timing generation unit includes an oscillation circuit and a multi-stage latch circuit, and each of the latch circuits generates a timing signal based on an oscillation output of the oscillation circuit. Laser control method. 5. 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, and this semiconductor laser. From the light receiving element for monitoring the optical output of the semiconductor laser and the light receiving signal proportional to the optical output of the semiconductor laser obtained from the light receiving element by forming an optical / electrical negative feedback loop together with the pulse width modulation / intensity modulation signal generating section. The semiconductor laser is driven by a current that is the sum or difference of the error amplification unit that controls the forward current of the semiconductor laser so that the given emission command signal becomes equal, and the control current of the optical / electrical negative feedback loop. A forward current to the semiconductor laser, which is generated so as to be controlled, is supplied to the semiconductor laser with a drive current according to a light emission command signal given from the pulse width modulation / intensity modulation signal generation unit A current driver for flowing, a differential quantum efficiency detector for detecting the differential quantum efficiency of the semiconductor laser, a timing generator for generating a timing signal for controlling the detection operation of the differential quantum efficiency detector at initialization, and the differential quantum A memory unit that stores the detection result at each timing of the efficiency detection unit, and an addition current setting unit that sets a current corresponding to the light emission command signal based on the detection result of the differential quantum efficiency detection unit stored in this memory unit, A semiconductor laser control device comprising: a bipolar transistor integrated as a one-chip integrated circuit. 6. The current drive unit is a voltage shift unit in the error amplification unit, is provided in the optical / electrical negative feedback loop including a differential circuit that changes the voltage shift amount, and the addition current setting unit is The optical output of the semiconductor laser has a desired maximum value when the current corresponding to the light emission command signal is maximum, and the optical output of the semiconductor laser has a desired minimum value when the current corresponding to the light emission command signal is minimum. It is assumed that the current of the differential circuit is set to, and at the time of initialization, the optical output of the semiconductor laser is set to a desired maximum value at a certain timing T0.
The optical output of the semiconductor laser is set to a desired minimum value at a timing T1 when a certain time has elapsed from 0, and the differential quantum efficiency detection unit is provided between the timing T1 and a timing T2 when a certain time has elapsed from the timing T1. 6. The semiconductor laser control device according to claim 5, wherein the addition current setting unit is operated to set the current. 7. The timing generator includes an external element,
6. The semiconductor laser control device according to claim 5, wherein the timing signal set by the external element is generated. 8. The semiconductor laser control device according to claim 5, wherein the timing generation section includes an oscillation circuit that generates a plurality of timing signals based on the oscillation output. 9. The semiconductor laser control device according to claim 5, wherein the timing generation section includes an oscillation circuit and a multi-stage latch circuit that generates each timing signal based on an oscillation output of the oscillation circuit.