JP3466599B1 - Semiconductor laser drive circuit and image forming apparatus - Google Patents

Abstract

An object of the present invention is to provide a high-speed and high-precision semiconductor laser drive circuit and an image forming apparatus. A drive current flowing through a semiconductor laser is composed of a sum current from four current sources, a bias current source, a threshold current source, a modulation current source, and a driving auxiliary current source. Among them, the bias current source 12 is 1 mA
It is several mA at most. The threshold current source 11 is a threshold current source at which the semiconductor laser 10 emits light. The threshold current source 11 may be a current (threshold current-bias current) obtained by subtracting the current value since the bias current source 12 flows. The modulation current source 13 is a current source that is modulated according to an input signal.
Light emission of 0 is controlled. The driving auxiliary current source 14 is an initial ON modulation current that has a magnitude proportional to the modulation current and is turned on in a short initial period when the modulation current is turned on.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser drive circuit and an image forming apparatus, and more particularly, to a semiconductor laser of a semiconductor laser used in a laser printer, an optical disk device, a digital copying machine, an optical communication device or the like. The present invention relates to a drive circuit and an image forming apparatus.

[0002]

2. Description of the Related Art Conventional semiconductor laser drive circuits are roughly classified into a non-bias type and a bias type. In the non-biased method, the bias current of the semiconductor laser is set to 0,
This is a method of driving a laser diode (hereinafter referred to as "LD") with a pulse current corresponding to an input signal. In the biased method, the bias current of the semiconductor laser is set to the threshold current of the semiconductor laser, and the bias is always applied. This is a method of driving a LD by applying a pulse current corresponding to an input signal to the bias current while flowing a current.

[0003]

By the way, when a semiconductor laser having a large threshold current is driven by a non-biased method, even if a driving current corresponding to an input signal is applied to the LD, carriers having a concentration capable of laser oscillation are generated. Since it takes a certain amount of time to generate a light emission delay, this does not cause a problem if the input signal is sufficiently larger than the light emission delay time (the light emission delay amount can be ignored), but a laser printer or an optical disk device The speeding up of digital copying machines and the like is rapidly advancing, and when it is desired to drive a semiconductor laser at a high speed, only a pulse smaller than a desired pulse width can be obtained.

Therefore, in order to reduce the time delay until the laser emission, a biased method in which the oscillation threshold current of the semiconductor laser is supplied in advance has been proposed. In this biased method, since the oscillation threshold current of the semiconductor laser is supplied in advance, the light emission delay time is eliminated, but even when light is not emitted, light is always emitted near the oscillation threshold (usually 200).
.mu.W to 300 .mu.W), the extinction ratio becomes small in the case of optical communication, and causes a background stain in the case of a laser printer, an optical disk device, a digital copying machine and the like.

In order to solve such a problem, in the field of optical communication, in JP-A-4-283978, JP-A-9-83050, etc., a bias-free method is basically used and immediately before light emission. A configuration has been proposed in which an oscillation threshold current is passed through. However, recently, in laser printers, optical disk devices, digital copying machines, etc.,
In pursuit of higher resolution, a 650 nm red LD,
Furthermore, a system using a 400 nm ultraviolet LD or the like has begun to be put into practical use. These semiconductor lasers are conventional 1.
Compared with LDs of 3 μm, 1.5 μm, and 780 nm band, it has a characteristic that it takes a longer time to generate carriers with a concentration capable of laser oscillation, and even in the above method, it is smaller than the desired pulse width. There is a problem that only the pulse width can be obtained.

Further, when trying to express a low density by a light output for a short time (for example, several ns or less), since the light emission output does not reach the peak intensity of the beam spot, the density becomes lower and the density cannot be expressed correctly. There was a problem. In order to solve this problem, JP-A-5-32807
In the invention described in Japanese Laid-Open Patent Publication No. 1-74, the density of the low density area is corrected by superimposing a differential pulse when the light rises. But,
In this method, since the peak of the differential pulse cannot be controlled, there is a high risk of destroying the semiconductor laser, and the time for superimposing the differential pulse also depends on the differential waveform.
Even if the initial extremely low density can be corrected, the gradation expression after that does not always increase linearly.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a high-speed and highly-accurate semiconductor laser drive circuit and an image forming apparatus.

[0008]

In order to solve the above problems, the present invention employs means for solving the problems having the following features.

According to a first aspect of the present invention, there is provided a bias current generating means for constantly supplying a minute bias current to the semiconductor laser, a threshold current generating means for supplying a threshold current to the semiconductor laser, and an input signal according to an input signal. A drive current generating unit that generates a drive current for driving the semiconductor laser to emit light, and a drive auxiliary current that causes a current to flow at the same time when the ON period of the drive current generating unit starts and then a current flows for a predetermined period. Having a driving auxiliary current generating means for generating,
The threshold current generation means generates a threshold current from the input signal, and the ON period of the threshold current generated by the threshold current generation means is longer than the light emission period of light emission by the drive current generation means, and the light emission is performed. It is a period including a period, and the semiconductor laser is driven by a sum current of four currents of the bias current, the drive current, the threshold current, and the drive auxiliary current.

According to the invention described in claim 1, a bias current generating means for constantly supplying a minute bias current to the semiconductor laser, a threshold current generating means for supplying a threshold current to the semiconductor laser, and an input signal In response to the drive current generating means for generating a drive current for driving the semiconductor laser to emit light, and a current flowing at the same time as the start of the ON period of the drive current generating means, and thereafter, a drive assist in which the current flows for a predetermined period. A driving auxiliary current generating means for generating a current, wherein the threshold current generating means generates a threshold current from the input signal, and the threshold current generated by the threshold current generating means is in the ON period for generating the drive current. Is longer than the light emission period for emitting light by the means and includes the light emission period, and includes the bias current, the drive current, the threshold current, and the drive supplement. By driving the semiconductor laser with a sum current of four currents, it is possible to provide a high-speed and highly-accurate semiconductor laser drive circuit that does not depend on the characteristics of the semiconductor laser and is excellent in gradation reproduction at low density. it can.

According to a second aspect of the present invention, in the semiconductor laser drive circuit according to the first aspect, the current generated by the bias current generating means generates a voltage of 1.5 V or less across the semiconductor laser. It is characterized in that it is an electric current.

According to the invention described in claim 2, the current generated by the bias current generating means is the minimum current for generating a voltage of 1.0 V to 1.5 V or more across the semiconductor laser. The impedance of the semiconductor laser can be sufficiently reduced with a small current,
Furthermore, since the current value is small, a sufficient extinction ratio can be secured,
Further, it is possible to provide a high-speed and high-accuracy semiconductor laser drive circuit which does not depend on the characteristics of the semiconductor laser and is excellent in gradation reproduction at low density.

According to a third aspect of the present invention, in the semiconductor laser drive circuit according to the first aspect, the current generated by the bias current generating means is several mA or less. .

According to the invention described in claim 2, since the current generated by the bias current generating means is several mA or less, the extinction ratio can be sufficiently secured, and the characteristic does not depend on the characteristics of the semiconductor laser. Further, it is possible to provide a high-speed and highly accurate semiconductor laser drive circuit which is excellent in gradation reproduction at low density.

According to a fourth aspect of the present invention, in the semiconductor laser drive circuit according to the first aspect, first delay signal generating means for delaying the input signal for a predetermined time to generate a first delay signal, Drive current generating means for driving the semiconductor laser based on the first delay signal, the threshold current generating means for generating the threshold current from the input signal and the first delay signal, and the first delay Second delay signal generating means for delaying the signal by a predetermined time to generate a second delay signal, and drive auxiliary current generation for generating the drive auxiliary current by the first delay signal and the second delay signal. Means and are provided.

According to the invention described in claim 4, first delay signal generating means for delaying an input signal by a predetermined time to generate a first delay signal, and a semiconductor laser based on the first delay signal. Driving current generating means for driving the first delay signal, a threshold current generating means for generating a threshold current from the input signal and the first delay signal, and a second delay signal for delaying the first delay signal for a predetermined time. By providing the second delay signal generation means and the drive auxiliary current generation means for generating the drive auxiliary current by the first delay signal and the second delay signal,
It is possible to provide a high-speed and high-accuracy semiconductor laser drive circuit which does not depend on the characteristics of the semiconductor laser described in claim 1 and which is excellent in gradation reproduction at low density.

According to a fifth aspect of the present invention, in the semiconductor laser drive circuit according to the fourth aspect, the delay amount of the first delay signal generating means and the delay amount of the second delay signal generating means are respectively set. A semiconductor laser drive circuit, which can be set independently.

According to the invention described in claim 5, the first
Since the delay amount of the delay signal generating means and the delay amount of the second delay signal generating means can be set independently of each other, the characteristics of the semiconductor laser are accurately corrected and the characteristics of the semiconductor laser are not affected. Further, it is possible to provide a high-speed and highly accurate semiconductor laser drive circuit which is excellent in gradation reproduction at low density.

According to a sixth aspect of the present invention, in the semiconductor laser drive circuit according to the first aspect, first delay signal generating means for delaying the input signal for a predetermined time to generate a first delay signal, Drive current generating means for driving the semiconductor laser based on the first delay signal, the threshold current generating means for generating the threshold current from the input signal and the first delay signal, and the first delay signal Drive auxiliary current generating means for generating the drive auxiliary current based on a differentiated pulse obtained by differentiating.

According to the invention described in claim 6, a first delay signal generating means for delaying an input signal by a predetermined time to generate a first delay signal, and a semiconductor laser based on the first delay signal. A drive current generating means for driving, a threshold current generating means for generating a threshold current from an input signal and the first delay signal, and a drive for generating a drive auxiliary current based on a differential pulse obtained by differentiating the first delay signal. By providing the auxiliary current generating means, it is possible to provide a high-speed and high-accuracy semiconductor laser drive circuit which does not depend on the characteristics of the semiconductor laser described in claim 1 and which is excellent in gradation reproduction at low density. .

According to a seventh aspect of the invention, in the semiconductor laser drive circuit according to any one of the fourth to sixth aspects, the drive current of the threshold current generated by the threshold current generation means is turned off. Characterized by not turning off before.

According to the invention described in claim 7, since the threshold current generated by the threshold current generating means is not turned off before the driving current is turned off, the threshold on signal is given before the modulation signal. Since it is not turned off, it is possible to provide an LD drive circuit capable of accurately emitting light from the LD according to an input signal.

According to an eighth aspect of the present invention, in the semiconductor laser drive circuit according to the first aspect, the magnitude of the drive auxiliary current is proportional to the drive current.

According to the invention described in claim 8, since the magnitude of the driving auxiliary current is proportional to the driving current, even if the differential quantum efficiency of the semiconductor laser changes, it is always safe and stable. In addition, it is possible to provide a concrete and easy-to-implement configuration of a high-speed and high-accuracy semiconductor laser driving circuit capable of achieving good reproduction of low-density gradation.

According to a ninth aspect of the present invention, in the semiconductor laser driving circuit according to the eighth aspect, the magnitude of the driving auxiliary current is smaller than the driving current.

According to the invention described in claim 8, since the magnitude of the driving auxiliary current is smaller than the driving current, the semiconductor laser is not destroyed or the life is shortened, and it is always safe and stable. In addition, it is possible to provide a concrete and easy-to-implement configuration of a high-speed and high-accuracy semiconductor laser driving circuit capable of achieving good reproduction of low-density gradation.

The invention described in claim 10 is claim 1
In the semiconductor laser drive circuit described above, a time during which the drive auxiliary current is turned on is 5 ns or less.

According to the tenth aspect of the present invention, since the driving auxiliary current is turned on for 5 ns or less, the semiconductor laser is not destroyed or its life is shortened. It is possible to provide a specific and easy-to-implement configuration of a high-speed and high-accuracy semiconductor laser driving circuit capable of stably reproducing low-density gradation.

The invention described in claim 11 is the same as claim 1.
In the semiconductor laser drive circuit described above, the drive current generating means has an initialization means that operates when the power is turned on or when reset is released, and the initialization means causes the light amount of the semiconductor laser to emit light at a predetermined value. It is set so that

According to the eleventh aspect of the present invention, the drive current generating means has an initialization means that operates when the power is turned on or when the reset is released, and the amount of light when the semiconductor laser emits light is set by the initialization means. By setting to a predetermined value, the amount of light emitted from the semiconductor laser at the beginning is set to a predetermined value, and a high-speed and high-precision LD drive and pulse that does not cause overshoot or the like with a simple configuration An LD drive circuit capable of outputting can be provided.

The invention described in claim 12 is the same as claim 1.
In the semiconductor laser drive circuit described in 1, the initialization means calculates a difference between a current or voltage when the light quantity of the semiconductor laser is a predetermined value and a current or voltage when the light quantity of the semiconductor laser is smaller than a predetermined value. It is characterized in that it is detected and set so that the amount of light emitted from the semiconductor laser becomes a predetermined value.

According to the twelfth aspect of the present invention, the initialization means includes a current or voltage when the light quantity of the semiconductor laser is a predetermined value and a current or voltage when the light quantity of the semiconductor laser is smaller than the predetermined value. By detecting the difference with the voltage and setting the light amount of the semiconductor laser at the time of light emission to a predetermined value, the initial light emission amount of the semiconductor laser is set to a predetermined value, and with a simple configuration. It is possible to provide an LD drive circuit that does not cause overshoot or the like and can perform LD drive and pulse output at higher speed and with higher accuracy.

The invention described in claim 13 is the same as claim 1.
In the semiconductor laser drive circuit described in 1, the initialization means detects a difference between a current or a voltage when the light intensity of the semiconductor laser is a predetermined value and a current or a voltage when the semiconductor laser is caused to emit an offset light. The amount of light emitted from the semiconductor laser is set to a predetermined value.

According to the thirteenth aspect of the present invention, the initialization means sets the difference between the current or voltage when the light amount of the semiconductor laser is a predetermined value and the current or voltage when the semiconductor laser is caused to perform offset light emission. Is detected and the amount of light emitted from the semiconductor laser is set to a predetermined value,
An LD which is set so that the amount of light emitted from an initial semiconductor laser has a predetermined value, does not cause overshoot and the like with a simple configuration, and is capable of higher-speed and highly-accurate LD driving and pulse output.
A driving circuit can be provided.

The invention described in claim 14 is the same as claim 1.
2. The semiconductor laser drive circuit according to 2, wherein the initialization means is a current or voltage when the light quantity of the semiconductor laser is a predetermined value, and the light quantity of the semiconductor laser is 1 / N of the predetermined value.
In the case of (N is a natural number of 2 or more), the difference from the current or the voltage is detected, and the light amount at the time of light emission of the semiconductor laser is set to a predetermined value.

According to the fourteenth aspect of the present invention, the initialization means includes the current or voltage when the light amount of the semiconductor laser is a predetermined value and the light amount of the semiconductor laser is 1 / N (N) of the predetermined value.
Is a natural number greater than or equal to 2) and the difference between the current and the voltage is detected, and the light amount of the semiconductor laser at the time of light emission is set to a predetermined value. Therefore, it is possible to provide an LD drive circuit which is set so as to have a simple structure and which does not cause overshoot or the like and which can perform LD drive and pulse output at higher speed and with higher accuracy.

The invention described in claim 15 is the same as claim 1.
In the semiconductor laser drive circuit according to 2 or 14, the initialization unit includes a timing generation unit, a detection unit that detects the difference, a current setting unit that sets the light amount of the semiconductor laser when emitting light, and the timing generation unit. It is characterized in that it is composed of a comparison unit that performs successive comparison so that the value detected by the detection unit based on the timing generated by the unit and the value set by the current setting unit correspond to each other.

According to the fifteenth aspect of the present invention, the initialization means includes a timing generation section, a detection section for detecting a difference, a current setting section for setting the light amount of the semiconductor laser when emitting light, and a timing generation. Since the value detected by the detection unit based on the timing generated by the unit and the value set by the current setting unit correspond to each other and the comparison unit performs successive comparison, the initial emission of the semiconductor laser It is possible to provide an LD drive circuit in which the amount is set to a predetermined value and which does not cause overshoot or the like with a simple configuration and which is capable of higher-speed and higher-accuracy LD drive and pulse output.

The invention described in claim 16 is the same as claim 1.
15. The semiconductor laser drive circuit according to any one of claims 1 to 15, wherein based on a light receiving section that detects a light output of the semiconductor laser and a light receiving signal proportional to the light output of the semiconductor laser detected by the light receiving section, It is characterized by having a current control means for controlling the current supplied to the semiconductor laser.

According to the sixteenth aspect of the invention, the semiconductor laser is detected based on the light receiving section for detecting the light output of the semiconductor laser and the light receiving signal proportional to the light output of the semiconductor laser detected by the light receiving section. By having the current control means for controlling the supplied current, it is possible to provide an LD drive circuit that can obtain a stable output even if there is a change over time due to temperature or the like.

The invention described in claim 17 is the same as claim 1.
In the semiconductor laser drive circuit described in 6, the current control means samples the control signal when the drive current generation means is in an on state, and controls the threshold current generation means based on the sampled value. Characterize.

According to the seventeenth aspect of the present invention, the current control means samples the control signal when the drive current generation means is in the on state, and controls the threshold current generation means based on the sampled value. As a result, it is possible to provide an LD drive circuit that can obtain a stable output even if there is a change with time due to temperature or the like.

The invention described in claim 18 is claim 1
In the semiconductor laser drive circuit described in 6, the voltage of the output unit that drives the semiconductor laser is detected, and the voltage of the power supply supplied to the semiconductor laser is controlled based on the detected value.

According to the eighteenth aspect of the present invention, the voltage of the output section for driving the semiconductor laser is detected, and the voltage of the power supply to be supplied to the semiconductor laser is controlled based on the detected value. Therefore, it is possible to provide an LD drive circuit that drives a large number of LDs.

According to a nineteenth aspect of the present invention, a semiconductor laser, the output of which is modulated by an image modulation signal, and a scanning means for scanning the rotating photosensitive member with the light of the semiconductor laser,
An image forming apparatus for forming an electrostatic latent image on the rotating photoconductor according to the image modulation signal, wherein the semiconductor laser is driven by the semiconductor laser drive circuit according to any one of claims 1 to 18. And

According to the nineteenth aspect of the present invention, the semiconductor laser whose output is modulated by the image modulation signal, the scanning means for scanning the rotary photoconductor with the light of the semiconductor laser, and the image modulation on the rotary photoconductor. An image forming apparatus for forming an electrostatic latent image according to a signal, wherein the semiconductor laser driving circuit according to any one of claims 1 to 18 drives the semiconductor laser to output a pulse at higher speed and with higher accuracy. It is possible to realize an image forming apparatus capable of performing the above.

The invention described in claim 20 is the same as claim 1.
In the image forming apparatus described in Item 9, the shading correction is performed by changing the full-scale value of the drive current generator according to the scanning of the scanning unit.

According to the twentieth aspect of the present invention, by performing the shading correction by changing the full-scale value of the drive current generator in accordance with the scanning of the scanning means, more accurate dots can be obtained. It is possible to realize an image forming apparatus capable of reproducing the above, and capable of high-speed and highly accurate pulse output.

[0049]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention focuses on the characteristics of LDs,
This is a method of driving a semiconductor laser with a sum current of three currents of a bias current, an oscillation threshold current and a light emission current. The bias current in the present invention is a very small amount of current, unlike the bias current in the biased method described above. The characteristics of the semiconductor laser are that the impedance is considerably large in the non-biased state, and even if a threshold current is flown from this state, it does not go to a level where the light emission delay time immediately disappears due to the influence of the inductance component in the semiconductor laser. If a current is applied to the semiconductor laser even at about 1 mA, the impedance of the semiconductor laser is considerably lowered. Therefore, if a threshold current is applied from this state, the light emission delay time is easily eliminated, and a very small bias is applied. Effective even with electric current.

Further, since the amount of light emitted from the semiconductor laser by the bias current of the present invention is at a sufficiently small level, as described above, the extinction ratio may be small in the case of optical communication which causes a problem in the biased system. In addition, even when it is applied to a laser printer, an optical disc device, a digital copying machine, etc., it does not cause a background stain.

In addition, by superimposing a current proportional to the light emission current at the beginning of the LD lighting start and controlling the light emission amount and the light emission time, it is safe without destroying the LD. It is possible to configure a semiconductor laser drive circuit and an image forming apparatus that can realize a linear density change from a low density to a characteristic LD.

Next, embodiments of the present invention will be described with reference to the drawings. (Basic Structure of the Present Invention) A basic conceptual diagram (basic structure) of the present invention is shown in FIG. In FIG. 1, a basic conceptual diagram of the present invention is first shown.
Shown in the figure. The configuration of FIG. 1 will be described. Semiconductor laser 10
As shown in the figure, the drive current supplied to the transistor has a magnitude proportional to the threshold current source 11, the bias current source 12, the modulation current source 13, and the modulation current, and has a short initial time (for example, 0. It is composed of a sum current of four currents of the initial on-modulation current (driving auxiliary current) source 14 which is turned on for 5 ns to 5 ns. Of these, the bias current source 12 is 1 mA.
It is several mA at most. The threshold current source 11 is a current source that supplies a threshold value at which the semiconductor laser 10 emits light. Figure 1
Since a bias current is flowing by the bias current source 12, a current value obtained by subtracting the current value (threshold current-bias current) may be used.

Here, regarding the bias current source, as shown in FIG.
This will be described with reference to FIG. 2 and 3 show the output P (μW) and the LD drop voltage VL when a small current is passed through a certain LD.
The actual measurement result of DDOWN is shown. Looking at FIG. 2 and FIG.
LD drop voltage VLDDOWN has LD current ILD of 250
About 1.4V has already been generated at μA, and gradually increases as ILD increases. Since LD has a DC resistance component, VLDDOWN gradually increases as ILD increases. When ILD is 0, VLDDOWN is 0, while when ILD is 250 μA, VLDDOWN is
It can be seen that N of 1.4 V is generated, and the impedance of the LD is sufficiently small only by applying 250 μA to the ILD. Accordingly, it can be predicted that the response characteristic is sufficiently improved by passing the threshold current after passing 250 μA. As predicted, according to the experiment, for example, by supplying a minute bias current of about 1 mA to the LD, the drop voltage change of the LD is small and the LD responds at high speed. Further, the light emission output of the LD at this time is 1.26 μW even at 1 mA, which is about 0.1% when considering that the normal LD light emission amount is 1 mW or more, which is an extinction ratio in optical communication and a laser. It can be seen that the level is such that the background stain does not occur in the printer and the digital copying machine. In addition, even if it has one PD (photodiode) and many LDs like an LD array, one L
With respect to the control of the amount of light of D, it does not matter that the other LD emits a weak light of about 1 μW. 2 and 3, the characteristics of a certain LD are actually measured and described as an example, but other LDs also show similar characteristics. (First Configuration: Generation of Control Signal of Threshold Current Source) FIG. 4 shows a first configuration example of the present invention. The configuration of FIG.
Threshold current source 11, bias current source 12, modulation current source 1
3, initial ON modulation current source 14, PD (photodiode)
20 and a differential amplifier 21.

The configuration of FIG. 4 shows an example of the configuration for generating the control signal of the threshold current source. LD threshold current source 11
Changes greatly with temperature, so as described later,
The threshold current source is always controlled by using the sample hold circuit. In FIG. 4, the output voltage of the PD 20 for detecting the optical output of the semiconductor laser 10 is compared with the emission control voltage, and
The threshold current source 11 is controlled so that the output of 0 and the emission control voltage match.

On the other hand, the bias current source 12 may be a fixed minute current, and the modulation current source 13 and the initial on-modulation current source 14 can be set to the temperature if the characteristic peculiar to the LD is measured and set at the time of initial setting. Since there is little change due to, a fixed current may be used as well.

With such a structure, it is possible to provide a high-speed and highly accurate semiconductor laser drive circuit. (Second Configuration) FIG. 5 shows a second configuration example of the present invention. The configuration of FIG. 5 has an LD 10, a threshold current source 11, a bias current source 12, a modulation current source 13, an initial-on modulation current source 14, and P.
D20, a differential amplifier 21, and switch circuits 31 to 33.

In FIG. 5, when the threshold ON signal is applied to the switch circuit 31, the current of the threshold current source 11 is supplied to the LD 10. Similarly, when the modulation signal is applied to the switch circuit 32, the current of the modulation current source 13 is supplied to the LD 10. Similarly, when the initial ON signal is applied to the switch circuit 33, the current of the initial ON modulation current source 14 is supplied to the LD 10. 6 and 7 show examples of timings of the modulation signal, the threshold ON signal, and the initial ON modulation signal in FIG.

FIG. 6 shows a light emission command signal (A), a first delay pulse (B) of the light emission command signal, a second delay pulse (C) of the light emission command signal, a modulation signal (D), and a threshold value ON signal. (E),
The initial ON modulation signal (F), the LD drive current (G), and the optical output waveform (H) which is the LD output are shown. Although not shown in FIG. 5, for example, the light emission command signal (A) input from the outside is delayed by the delay circuit to become the first delay pulse (B) and the second delay pulse (C). Further, the first delay pulse signal becomes the modulation signal (D), the logical sum of the light emission command signal (A) and the first delay pulse (B) becomes the threshold ON signal (E), and the first delay pulse ( Second, which is the reverse of B)
ANDed with the delayed pulse (C) is the initial ON modulation signal (F).

The delay circuit used to generate the signal is
For example, it may be simply performed by an inverter train or a buffer train, or a signal whose waveform is shaped after being delayed by a low-pass filter including a resistor and a capacitor may be used. In either case, changing the delay amount can be easily performed by changing the number of stages or the filter constant.

At this time, the LD drive current (G) is the sum of four currents of bias current + threshold current + modulation current + initial ON modulation current. The threshold current is 1 to 1 of the modulation current.
It is configured to turn on 0 ns before and turn off simultaneously with the modulation current. The time difference between the threshold current and the modulation current is originally preferably as short as possible, but assuming an actual laser printer or digital copying machine, even if the threshold light emission is performed for about 1 dot or less, that portion is slightly There is no problem because it causes only dirt. When a red LD or an ultraviolet LD is used, it has a characteristic that it takes time to generate a carrier having a concentration capable of laser oscillation, as compared with an infrared LD. It may be necessary to pass the threshold current before. However, LD
The driver is ASIC (Application Spe
In the case of making the IC (Cic IC), it is possible to freely set the time for flowing the threshold current if the delay driver has a function of controlling the delay time from the outside. realizable.

Regarding the initial on-modulation current, as described above, the modulation current is on for a short initial time (for example, 0.5 ns to 5 ns).
In the case of a laser printer or the like, the sensitivity characteristic of the photoconductor may be taken into consideration, and the time may be set so that the gradation reproducibility is the best. Also, its size (A times the modulation current) is L
The setting is performed in consideration of the characteristics of D and the sensitivity characteristics of the photoconductor.
For example, usually, A is set to about 0.1 to 1. Further, if A is set larger than this, the light amount exceeds the rating of the LD, there is a high risk of destroying the LD, and there is a problem in terms of the life and safety of the LD.

FIG. 7 shows an example in the case of a drive current different from that in FIG. In FIG. 7, as in FIG. 6, the light emission command signal (A),
First delay pulse (B) of light emission command signal, second delay pulse (C) of light emission command signal, modulation signal (D), threshold on signal (E), initial on modulation signal (F), LD drive current (G)
And the optical output waveform (H) which is the LD output is shown.

In FIG. 7, the threshold current is turned off after the modulation signal for the threshold on signal is turned off. Normally, even if it is said that the threshold value ON signal and the modulation signal are turned off at the same time, it is difficult to turn them off at the same timing at high speed. Therefore, the threshold value ON signal is turned off after confirming that the modulation signal is turned off. However, the difference is several nanoseconds at the most, and even when a laser printer or a digital copying machine is assumed, the background stain is generated in only a few nanoseconds, so there is no problem on the image. With this configuration, the threshold on signal does not turn off before the modulation signal,
An LD drive circuit that can accurately output a pulse can be realized. (Initial setting of modulation current source) Voltage VLD across LD10 when LD10 is at full power (maximum power: P0)
_FULL (the current flowing in the LD at that time is I _OP ) and the LD 10 when the threshold current starts flowing
When the voltage VLD _TH between both ends of (the current flowing in the LD at that time is I _TH ) is defined as VLD _D (= VLD _FULL −VLD _TH ), the difference between these currents is defined as VLD _D (= VLD _FULL −VLD _TH ). I and _{D (= I OP -I T H} ). At that time, the current value of the modulation current source is changed to (I _D (= I _OP −
I _TH ). When setting with voltage, VLD
_D (= VLD _FULL -VLD _TH ) is used.

At this time, the optimum current value of the modulation current source is
(I _D (= I _OP −I _TH ). That is, when the current value of the modulation current source is (I _OP −I _TH ), the current of the threshold current source 11 (I _TH ) and the LD emits light with full power, and in this case, the LD is combined with the current of the threshold current source 11 and the LD emits light with full power. It can be said that it is the lowest modulation current, and the consumption of current is the least.Also, even if it is combined with the current of the threshold current source 11 and the bias current source, the current flowing in the LD is I _OP , Excessive current is not supplied to the LD, and the life of the LD can be extended.

In this way, the circuit of FIG. 8 is used to set the optimum current value of the modulation current source. The circuit of FIG.
When the power supply voltage is turned on (or when the LD is turned off), the differential quantum efficiency of the LD (gradient characteristic of the output power with respect to the LD current (differential characteristic)) is detected, and the modulation current is initialized based on the characteristic. It is a circuit for.

FIG. 8 shows a timing generation section 51, a differential quantum efficiency detection section 52, a D / A (digital / analog conversion) section 5.
3, the current detector 71, the modulation current source 13 and the LD 10. The timing generation unit 51 generates a timing signal at a predetermined timing. Differential quantum efficiency detector 5
2 performs setting processing in accordance with the timing from the timing generation unit 51. The differential quantum efficiency detection unit 52 is
A current setting unit (not shown) that sets the light amount of the semiconductor laser at the time of light emission to the D / A unit 53, a current or a voltage when the light amount of the semiconductor laser has a predetermined value, and the light amount of the semiconductor laser is 1 / N (N is a natural number of 2 or more), a detection unit (not shown) that detects a difference from the current or the voltage, a value detected by the detection unit, and a value set by the current setting unit Correspondingly, it is configured with a comparison unit (not shown) that performs successive comparison, and the setting process is performed by two methods described in detail below. The D / A unit 53 uses the differential quantum efficiency detection unit 52 to
The digital signal for setting the output current value of the modulation current source is converted into an analog signal to control the current value of the modulation current source 13.

Next, two methods of setting the modulation current in the differential quantum efficiency detection section 52 will be described.

The first method will be described with reference to FIGS. 9 and 10. FIG. 9 is a diagram showing a differential quantum efficiency characteristic of an LD. When the current supplied to the LD increases and reaches a current value I _TH , the LD starts to emit light (the voltage applied to the LD at that time is VLD. _TH , and the output power of the LD at that time is P _TH ). The current that outputs the maximum power P _O determined by the standard is I _OP (the voltage applied to the LD at that time is VLD _OP ).

FIG. 10A shows the timing signal LVCO from the timing generator 51, and FIG. 10B shows the LD signal.
10C shows an analog setting signal output from the D / A. Note that FIG. 10 (C)
The value of is an example and is not limited to this.

The timing generator 51 operates only at the time of initialization, and the timing signal LVC shown in FIG.
O is supplied to the differential quantum efficiency detection unit 52. The differential quantum efficiency detection unit 52, based on the timing signal LVCO,
10 timings from = 0 to T = 9 are generated. The differential quantum efficiency detection unit 52 performs processing according to each timing, and outputs an 8-bit value to the D / A unit 53 in synchronization with the timing from the timing generation unit 51. D
/ A section 53, for example, 1, 0.5, 0.25, 0.
Values such as 125 are output in descending order.

The differential quantum efficiency detector 52, at T = 0,
The LD is forcibly turned on (full power lighting), the LD is caused to perform offset light emission (near I _TH ) at T = 1, and the LD is turned off (at a bias current of about 1 mA) at T = 9. Also, T =
At 1, the difference of I _OP −I _TH is held. On the other hand, in accordance with the timing from the timing generation unit 51, the D / A unit 53 causes T = 0 to T = 9 to be 1, 0.5,
Values such as 0.25, 0.125, etc. are output in order. Here, for example, the difference of I _OP −I _TH is 0.7 mA, and the value of the D / A unit 53 is 1, 0.5, 0.25, 0.1.
25 etc. is 1 mA, 0.5 mA, 0.25 mA, 0.1
The following description will be given on the assumption that the modulation current source 13 is controlled so as to correspond to 25 mA or the like.

At T = 2, the output of 1 is applied to the modulation current source 13 from the D / A section 53, and 1 mA is output from the modulation current source 13.
Current flows. The current detector 71 detects this current,
The differential quantum efficiency detection unit 52 compares this 1 mA with the held 0.7 mA. As a result, 1mA> 0.7
Since it is mA, the differential quantum efficiency detection unit 52 ignores "1" and prepares for the next timing.

At T = 3, an output of 0.5 is applied to the modulation current source 13 from the D / A section 53, and a current of 0.5 mA flows from the modulation current source 13. This current is detected by the current detector 71.
Is detected by the differential quantum efficiency detection unit 52.
Is compared with the held 0.7 mA. As a result, since 0.5 mA <0.7 mA, the differential quantum efficiency detection unit 52 sets “0.5” and prepares for the next timing.

At T = 4, an output of 0.25 is applied to the modulation current source 13 from the D / A section 53, and a current of 0.25 mA flows from the modulation current source 13. This current is detected by the current detection unit 7
1 is detected by the differential quantum efficiency detection unit 52.
"0.5m" corresponding to mA and "0.5" set earlier
A) 0.75 mA summed with “A” is compared with the held 0.7 mA. As a result, 0.75 mA> 0.
Since it is 7 mA, the differential quantum efficiency detection unit 52 displays “0.
5 ”is ignored and the next timing is prepared.

When T = 5, the D / A section 53 outputs 0.125.
Is applied to the modulation current source 13, and a current of 0.125 mA flows from the modulation current source 13. The differential quantum efficiency detection unit 52 detects this current, and adds it to “0.5 mA” corresponding to “0.5” previously set to 0.6.
25 mA is compared with the held 0.7 mA. As a result, since 0.625 mA <0.7 mA, the differential quantum efficiency detection unit 52 sets “0.125” and prepares for the next timing.

When T = 6, the D / A section 53 outputs 0.062.
5 is applied to the modulation current source 13 and the modulation current source 13
A current of 0.0625 mA flows. This current is detected by the current detection unit 71, and the differential quantum efficiency detection unit 52 determines that this 0.0625 mA is “0.625 mA” corresponding to “0.5” and “0.125” previously set. The total of 0.6875 mA and the held 0.7 m
Compare with A. As a result, 0.6875 mA <0.7 m
Since it is A, the differential quantum efficiency detection unit 52 displays “0.06
25 "is set to prepare for the next timing.

At T = 7, from the D / A section 53, 0.031
The output of 25 is applied to the modulation current source 13,
A current of 3 to 0.03125 mA flows. The current detector 71 detects this current, and the differential quantum efficiency detector 52
"0.5" which is set with this 0.3125mA,
"0 .." corresponding to "0.125" and "0.0625".
6187 mA "and 0.71875 mA are compared with the held 0.7 mA. As a result, 0.
Since 71875 mA> 0.7 mA, the differential quantum efficiency detection unit 52 ignores "0.03125" and thereafter. In this way, the initial setting current value of the modulation current source is set to (I _OP −I _TH ). In this example, the differential quantum efficiency detection unit 52 sets the set “0.5”, “0.
The values “125” and “0.0625” are set as the output values of the D / A unit 53, and “0.6875 mA” corresponding to the output values.
Current flows from the modulation current source 13. That is, 0.6875 mA is set as the optimum current value of the modulation current source 13.

The above numerical values are examples. It can also be a rounded value. Further, although the example of FIG. 10 is a case where the D / A has an 8-bit configuration, the required timing number is changed depending on the number of bits configuring the D / A.

Further, in the case of this example, in order to obtain the threshold current I _TH at the time of initialization, setting is performed so that a desired offset light emission value is obtained from the external terminal, and a current source that operates only at the time of initialization is used. It may be provided. Further, the timing signal LVCO may be configured so that its timing can be adjusted by an external terminal.

The second method will be described with reference to FIGS. 11 and 12. Differs from the first method, as a value held in the differential quantum efficiency detection unit _52, instead of using the (I OP _{-I TH),} which is half the value of _{I OP I OP} '
With _{(I OP} / 2), in that using the _{(I O P '-I TH)} .

In the second method, the differential quantum efficiency detecting section 52 doubles the held (I _OP / 2-I _TH ) and the D / A section 53 from T = 2 to T = 9. Compare with the current corresponding to the value of. Other than that, since it is the same as the first method, description thereof will be omitted.

[0082] In the above description, the current value as a value held in the differential quantum efficiency detection unit 52 _(I OP _{-I TH)}
Or _{(I OP / 2-I TH} ) a was used, the current value _(I O P _{-I TH)} or _{(I OP / 2-I TH} ) to the corresponding LD voltage _(VLD FULL -VLD _TH) or ( V
LD _FULL / 2-VLD _TH ) may be used to initialize the modulation current source by the LD voltage.

In the first method, the LDs are driven in the descending order from the D / A section 53, for example, 1, 0.5, 0.25, 0.125, etc., and the comparison is performed. ing. As a result, since the initial value is large, there are cases where the LD is drastically exceeded the standard, and this may cause damage to the LD or shorten the life of the LD. However, in the second method, instead of using (I _OP −I _TH ), (I _OP /
2- _ITH ) does not cause such a problem. However, in the second method, (I _OP / 2-
Since I _TH ) is compared with a doubled value, the control accuracy is lower than that of the first method.

Using the circuit of FIG. 8, when the power is turned on or the reset is released, the optimum current value of the modulation current source is set based on the differential quantum efficiency of the LD. , D / A section 53. (Third Configuration: Generation of Threshold Current Source Control Signal) FIG.
The 3rd structural example of this invention is shown. The configuration of FIG. 13 is LD1
0, a threshold current source 11, a bias current source 12, a modulation current source 13, an initial ON modulation current source 14, a PD 20, a differential amplifier 21, switch circuits 31 to 33, and a sample & hold circuit 41. 5 is different from the configuration of FIG. 5 in that it has a sample & hold circuit 41 for sampling and holding at the timing of on / off of the modulation signal, and the output of this sample & hold circuit 41 controls the threshold current source 11. .

In FIG. 13, the output of the differential amplifier 21 is sampled and held when the modulation signal is ON, and when there is no modulation signal, the threshold current source 11 is controlled by the held signal. . With this configuration, for example, it is possible not only to adjust the light amount only outside the image writing area but also to perform sampling and control each time the LD 10 is turned on even in the writing area. (Fourth Configuration) FIG. 14 shows a fourth configuration example of the present invention.
The configuration of FIG. 14 has an LD 10, a threshold current source 11, a bias current source 12, a modulation current source 13, and an initial ON modulation current source 1.
4, PD 20, differential amplifier 21, switch circuits 31 to 3
3, sample & hold circuit 41, timing generator 5
1, differential quantum efficiency detector 52, D / A 53, delay circuit 5
4, threshold signal generator 55, delay circuit 56 and logic circuit 5
It is composed of 7.

FIG. 14 shows an example of a specific configuration example of the timing charts shown in FIGS. 6 and 7 when it is configured by a one-chip ASIC 50. In the configuration of FIG. 13, the point that the light emission command signal becomes the modulation signal through the delay circuit 54, the modulation signal A and the signal B through the delay circuit 56 are set to the logic circuit 5
In FIG. 7, a predetermined logic (A & (inversion B)) is performed to control the switch circuit 33, and a circuit for initializing the modulation current shown in FIG. 8 (timing generation unit 51, differential quantum efficiency detection unit) 52, D / A section 53, etc.) and the threshold signal generating section 55 generates a threshold ON signal by ORing the light emission command signal and the delay signal.

The threshold signal generator 55 and the delay circuit 54 are also provided.
By controlling the switch circuit 31, the switch circuit 32, and the switch circuit 33, respectively, the output signals of the logic circuit 57 and the logic circuit 57 can generate an LD drive current as shown in FIGS. 6 and 7. (Fifth Configuration) FIG. 15 shows a fifth configuration example of the present invention.
The configuration of FIG. 15 has an LD 10, a threshold current source 11, a bias current source 12, a modulation current source 13, and an initial ON modulation current source 1.
4, PD 20, differential amplifier 21, switch circuits 31 to 3
3, sample & hold circuit 41, timing generator 5
1, differential quantum efficiency detector 52, D / A 53, delay circuit 5
4, threshold signal generator 55, delay circuit 56, logic circuit 5
7, a VLD detection circuit 61 and a VLD control circuit 62. It differs from the configuration of FIG. 14 in that it has a shading correction function and an LD power supply (VLD) control function.

First, the shading correction function will be described. The differential quantum efficiency of the LD detected when the power is turned on or when the reset is released is set to D / A. This D / A
When the current or voltage that determines the full scale of the current is input from the external terminal and the full scale is changed, the light emission amount of the LD can be changed. For example, in an LD writing system that performs a raster scan, the energy density of the central portion is high, so that the scanning end has a large light emission amount and the central portion has a small light emission amount so that the LD light emission amount is inversely corrected. Correction (shading correction). The speed of this correction may be slow, as long as the change follows the time during which the LD scans one line. Shading correction is performed by changing the current value of the D / A by a signal that changes the amount of light emission as described above according to the time for scanning one line from the outside.

Next, the LD power source (VLD) control function will be described. The purpose of controlling VLD is to drive the LD drive unit to the ASIC.
Drive current of the LD is 10 depending on the LD.
Since it is necessary to pass a large current of about 0 mA, ASI
The power consumption as C is affected. For example, with a 5V power supply,
Assuming that the voltage drop of the LD is 2 V, the ASIC requires 100 mA at 3 V, that is, 300 mW with the LD current alone. When the number of LDs to drive is 2, 600mW only by the LD current, and when the number of LDs to drive is 4, L
The D current alone would require 1200 mW. Since it becomes difficult to drive a large number of LDs as they are, VLD is controlled. In the above example, for example, since the cathode portion of the LD has a voltage of 3V, the power consumption has increased, but if the cathode portion of the LD can be controlled to about 1V, the LD
The current consumption of the ASIC is 1/3. VLD
Detection of the threshold ON signal or the modulation signal detects the cathode potential of the LD when it is ON, and outputs a VLD control signal to the outside of the ASIC so that it becomes a certain desired voltage (for example, 1 V). VL
The D control signal is input to, for example, the base of the power transistor, and if the emitter of the power transistor is connected to the LD power source, VLD can be controlled. Since this control speed may be a speed sufficiently slower than the modulation speed of the LD, any power transistor may be used as long as it can supply a sufficient current to the LD. By having such a VLD control function, an LD drive circuit that consumes less power and can drive a large number of LDs can be realized. (Sixth Configuration) FIG. 16 shows a sixth configuration example of the present invention.
The configuration of FIG. 16 has an LD 10, a threshold current source 11, a bias current source 12, a modulation current source 13, and an initial ON modulation current source 1.
4, PD 20, differential amplifier 21, switch circuits 31 to 3
3, sample & hold circuit 41, timing generator 5
1, differential quantum efficiency detector 52, D / A 53, delay circuit 5
4, a threshold signal generator 55, a differentiation circuit 58, a VLD detection circuit 61, and a VLD control circuit 62. The configuration is different from the configuration of FIG. 15 in that the delay circuit 56 and the logic circuit 57 are replaced with a differentiating circuit 58.

The differentiating circuit 58 differentiates the modulated signal output from the delay circuit 54, and controls the switch circuit 33 with the output.

FIG. 17 shows the timing of generation of the LD drive current (G). The light emission command signal (A) is applied to the delay circuit 54, and the delay pulse (B) of the light emission command signal is obtained as its output. Delay pulse (B) of this light emission command signal
Becomes a modulated signal (D). The delay pulse (B) of the light emission command signal is applied to the differentiating circuit 58. A differential pulse (C) of the light emission command signal is output from the differentiating circuit 58, and the output signal controls the switch circuit 33. The differential pulse (C) of the light emission command signal has a differential pulse at the time of rising and a differential pulse at the time of falling. The switch circuit 33 is controlled by a differential pulse larger than ΔC in the enlarged view of the differential pulse at the time of rising. As a result, the switch circuit 33 is turned on only during the ΔT period, and the initial ON modulation current (F) flows from the initial ON modulation current source 14.

With the configuration shown in FIG. 17, the LD drive current
(G) can flow the same current as that shown in FIGS. 6 and 7.

An image forming apparatus can be constructed by using the semiconductor laser driving circuit described above. For example,
A semiconductor laser whose output is modulated by an image modulation signal, and scanning means for scanning the rotating photoconductor with the light of the semiconductor laser.
In an image forming apparatus having an electrostatic latent image forming means (not shown) and an electrostatic latent image forming means for forming an electrostatic latent image according to an image modulation signal on a rotating photoconductor, the semiconductor laser driving circuit described above drives the semiconductor laser. As a result, an image forming apparatus including a high-speed and highly accurate semiconductor laser drive circuit can be configured.

[0094]

As described above, according to the present invention, it is possible to provide a high-speed and highly accurate semiconductor laser drive circuit and image forming apparatus.

[0095]

[Brief description of drawings]

FIG. 1 is a diagram for explaining a basic conceptual diagram (basic configuration) of the present invention.

FIG. 2 is a diagram (No. 1) for explaining the characteristics of LEDs.

FIG. 3 is a diagram (part 2) for explaining the characteristics of the LED.

FIG. 4 is a diagram for explaining a first configuration example of the present invention.

FIG. 5 is a diagram for explaining a second configuration example of the present invention.

FIG. 6 is a modulation signal, a threshold ON signal, an initial ON modulation signal,
It is a figure for demonstrating the relationship (1) of LD drive current and LD output.

FIG. 7 is a modulation signal, a threshold ON signal, an initial ON modulation signal,
It is a figure for demonstrating the relationship (2) of LD drive current and LD output.

FIG. 8 is a diagram for explaining a configuration example for initial setting of a modulation current source.

FIG. 9 is a diagram (No. 1) for explaining the first method of initial setting of the modulation current source.

FIG. 10 is a diagram (No. 2) for explaining the first method of initial setting of the modulation current source.

FIG. 11 is a diagram (No. 1) for explaining the second method of initial setting of the modulation current source.

FIG. 12 is a diagram (No. 2) for explaining the second method of initial setting of the modulation current source.

FIG. 13 is a diagram for explaining a third configuration example of the present invention. .

FIG. 14 is a diagram illustrating a fourth configuration example of the present invention.

FIG. 15 is a diagram illustrating a fifth configuration example of the present invention.

FIG. 16 is a diagram for explaining a sixth configuration example of the present invention.

FIG. 17 is a diagram for explaining a relationship (part 3) between a modulation signal, a threshold ON signal, an initial ON modulation signal, an LD drive current, and an LD output.

[Explanation of symbols]

10 Laser diode (LD) 11 Threshold current source 12 Bias current source 13 Modulated current source 14 Initial ON modulation current source (driving auxiliary current source) 20 Photodiode (PD) 21 Differential amplifier 31, 32, 33 switch circuit 41 Sample and hold circuit 50 ASIC 51 Timing generator 52 Differential quantum efficiency detector 53 D / A section 54, 56 Delay circuit 55 Threshold signal generator 57 Logic circuit 61 VLD controller 62 VLD detector

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasushi Nihei 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (56) Reference JP-A-4-283978 (JP, A) JP Japanese Unexamined Patent Publication No. 9-83050 (JP, A) Japanese Unexamined Patent Publication No. 5-328071 (JP, A) Japanese Unexamined Patent Publication No. 2003-60289 (JP, A) Japanese Unexamined Patent Publication No. 2003-101131 (JP, A) Japanese Unexamined Patent Publication No. 10-119350 (JP, A) ) JP 2000-164972 (JP, A) JP 10-209538 (JP, A) JP 5-136501 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01S 5/00-5/50 B41J 2/44

Claims (20)

(57) [Claims] 1. A bias current generating means for constantly supplying a minute bias current to the semiconductor laser, a threshold current generating means for supplying a threshold current to the semiconductor laser, and causing the semiconductor laser to emit light according to an input signal. Driving current generating means for generating a driving current for driving, and a current flows simultaneously with the start of the ON period of the driving current generating means, and thereafter,
For a predetermined period, it has a drive auxiliary current generating means for generating a drive auxiliary current through which a current flows, the threshold current generating means generates a threshold current from the input signal, and the threshold current generated by the threshold current generating means. The ON period of is longer than the light emitting period for emitting light by the drive current generating means, and is a period including the light emitting period, and includes four currents of the bias current, the drive current, the threshold current, and the drive auxiliary current. A semiconductor laser drive circuit, characterized in that the semiconductor laser is driven by a sum current. 2. The semiconductor laser drive circuit according to claim 1, wherein the current generated by the bias current generating means is
A semiconductor laser drive circuit having a minimum current for generating a voltage of 1.0 V to 1.5 V or more across the semiconductor laser. 3. The semiconductor laser drive circuit according to claim 1, wherein the current generated by the bias current generating means is
A semiconductor laser drive circuit characterized by being several mA or less. 4. The semiconductor laser drive circuit according to claim 1, wherein the input signal is delayed by a predetermined time to generate a first delay signal, and based on the first delay signal. Drive current generating means for driving the semiconductor laser, the threshold current generating means for generating the threshold current from the input signal and the first delay signal, and delaying the first delay signal for a predetermined time. A second delay signal generating means for generating a second delay signal; and a drive auxiliary current generating means for generating the drive auxiliary current by the first delay signal and the second delay signal. A characteristic semiconductor laser drive circuit. 5. The semiconductor laser drive circuit according to claim 4, wherein the delay amount of the first delay signal generating means and the delay amount of the second delay signal generating means can be set independently of each other. A characteristic semiconductor laser drive circuit. 6. The semiconductor laser drive circuit according to claim 1, wherein the input signal is delayed by a predetermined time to generate a first delay signal, and based on the first delay signal. Based on drive current generation means for driving the semiconductor laser, the threshold current generation means for generating the threshold current from the input signal and the first delay signal, and a differential pulse obtained by differentiating the first delay signal. A drive auxiliary current generating means for generating the drive auxiliary current. 7. The semiconductor laser drive circuit according to claim 4, wherein the threshold current generated by the threshold current generation means is not turned off before the drive current is turned off. Semiconductor laser drive circuit. 8. The semiconductor laser drive circuit according to claim 1, wherein the magnitude of the drive auxiliary current is proportional to the drive current. 9. The semiconductor laser drive circuit according to claim 8, wherein the magnitude of the drive auxiliary current is smaller than the drive current. 10. The semiconductor laser drive circuit according to claim 1, wherein the drive auxiliary current is turned on for 5 ns or less. 11. The semiconductor laser drive circuit according to claim 1, wherein the drive current generation means has an initialization means that operates when power is turned on or reset is released, and the initialization means emits light from the semiconductor laser. A semiconductor laser drive circuit, wherein the amount of light at time is set to a predetermined value. 12. The semiconductor laser drive circuit according to claim 11, wherein the initialization unit is a current or a voltage when the light amount of the semiconductor laser is a predetermined value, and a current or voltage when the light amount of the semiconductor laser is less than a predetermined value. Detects the difference from the current or voltage,
A semiconductor laser drive circuit, characterized in that the amount of light emitted from the semiconductor laser is set to a predetermined value. 13. The semiconductor laser drive circuit according to claim 11, wherein the initialization unit has a current or a voltage when the light intensity of the semiconductor laser has a predetermined value and a current or a voltage when the semiconductor laser emits an offset light. A semiconductor laser drive circuit, wherein a difference from a voltage is detected and the amount of light emitted from the semiconductor laser is set to a predetermined value. 14. The semiconductor laser drive circuit according to claim 12, wherein the initialization means is a current or a voltage when the light quantity of the semiconductor laser is a predetermined value, and the light quantity of the semiconductor laser is 1 / N of the predetermined value. A semiconductor laser driving circuit, wherein a difference from a current or a voltage in the case of (N is a natural number of 2 or more) is detected, and the light amount of the semiconductor laser at the time of light emission is set to a predetermined value. 15. The semiconductor laser drive circuit according to claim 12, wherein the initialization unit includes a timing generation unit, a detection unit that detects the difference, and a current that sets a light amount when the semiconductor laser emits light. It is composed of a setting unit and a comparison unit that performs successive comparison so that the value detected by the detection unit based on the timing generated by the timing generation unit and the value set by the current setting unit correspond to each other. A semiconductor laser drive circuit characterized by the above. 16. The semiconductor laser drive circuit according to claim 1, wherein the light receiving unit detects an optical output of the semiconductor laser, and the optical output of the semiconductor laser is detected by the light receiving unit. A semiconductor laser drive circuit comprising a current control means for controlling a current supplied to the semiconductor laser based on the received light receiving signal. 17. The semiconductor laser drive circuit according to claim 16, wherein the current control unit samples the control signal when the drive current generation unit is in an ON state, and the threshold current is based on the sampled value. A semiconductor laser drive circuit characterized by controlling a generation means. 18. The semiconductor laser drive circuit according to claim 16, wherein the voltage of the output section that drives the semiconductor laser is detected, and the voltage of the power supply supplied to the semiconductor laser is controlled based on the detected value. Semiconductor laser drive circuit. 19. A semiconductor laser whose output is modulated by an image modulation signal, scanning means for scanning the rotating photoconductor with the light of the semiconductor laser, and electrostatic latent image on the rotating photoconductor according to the image modulation signal. An image forming apparatus for forming an image, wherein the semiconductor laser is driven by the semiconductor laser driving circuit according to any one of claims 1 to 18. 20. The image forming apparatus according to claim 19, wherein the shading correction is performed by changing a full scale value of the drive current generation unit according to scanning of the scanning unit. apparatus.