JP2000114649A - Laser driver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an accurate laser emission duty ratio by providing an error detector which acts so that the output of a light power detecting means is equal to that of a light power setting means upon receipt of a clock of a specified period as a picture signal and holds an output voltage. SOLUTION: A video signal composed of a trains of on-off pulses including specified rise and fall times is inputted to an inversion terminal of a high-speed differential amplifier 12. A sample holding circuit 13 is provided for storing the mean light quantity in the on/off-time of a laser to input it to a noninversion terminal of the different amplifier 12. While the peak light quantity of the laser is stored in a sample holding circuit 14 and the mean light quantity in the on/off-time of the laser is stored in the sample holding circuit 13 under the feed back control, data are inputted to a video signal line to obtain a stable on-off duty ratio of a laser diode 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a laser driving apparatus for driving a semiconductor laser applicable to a laser beam printer, a magneto-optical disk, and the like.

[0002]

2. Description of the Related Art In recent years, laser beam printers have achieved high resolution.
It is widely accepted in the market as a high-speed printer.
Further demands for higher resolution and higher speed are increasing.

An important factor in increasing the resolution and speed of the laser beam printer is the high-speed response of the semiconductor laser driving device. For example, 16 sheets of A4 size paper are printed every minute, and the resolution is set to 600 × 600 (d
pi), the modulation frequency of the semiconductor laser is 17M
Hz.

On the other hand, the peak of the driving current of the semiconductor laser needs to be about 30 mA to 100 mA. When switching such a large current, it is difficult to keep the rise time and fall time of the laser drive current low.

Accordingly, the ratio of the rise time and the fall time to the modulation period is large, and as a result, the laser current waveform is different from a square wave, and becomes a distorted waveform as integrated.

[0006] The current vs. light amount characteristics of a semiconductor laser is as follows.
It has a characteristic like a secondary characteristic curve. In this case, the current It of the semiconductor laser is a current at which the semiconductor laser starts laser oscillation, and is called a threshold current of the laser.

In a region where the semiconductor laser is equal to or larger than the threshold current It, the amount of laser light changes almost linearly with respect to the laser current. The slope in that region is the slope efficiency (mW / m
A).

In the semiconductor laser having such characteristics, the light amount waveform rapidly rises in the case of a low-speed rise with respect to the current value of the laser current. Characteristic dullness occurs. Further, when comparing the period ton during which the laser current emits light with the period toff during which the laser does not emit light, ton is clearly shorter than toff.

The reason is that the time required for the rise and fall of the laser current occupies a considerable proportion of the laser modulation period. This becomes more remarkable as the laser drive current frequency increases.

[0010]

As described in the prior art, the higher the laser driving frequency, the higher the laser emission duty ratio (= Ton / (Ton + Toff)).
Has the disadvantage that it becomes smaller.

In addition, the threshold current It and the slope efficiency of a semiconductor laser often vary greatly depending on the lot of the laser, and this has the disadvantage that the duty ratio of laser emission also varies greatly.

Furthermore, the higher the laser drive frequency, the greater the variation between the rising current and the falling current of the laser drive circuit, which affects the duty ratio.
Therefore, there is a disadvantage that the duty ratio of laser emission greatly varies due to lot variation in a laser drive (laser drive) circuit. Also, when the laser drive frequency is increased, the rise time and the fall time of the image signal input to the laser drive circuit cannot be ignored compared to the laser drive cycle. Affects duty ratio.

Therefore, in view of the above, the present invention is configured so that an accurate laser light quantity output of a laser emission duty ratio can always be obtained irrespective of a semiconductor laser characteristic and a high frequency characteristic of a drive circuit for driving the laser current. It is an object of the present invention to provide a laser drive device that has been developed.

[0014]

In order to achieve the object of the present invention, the present invention provides a first optical power detecting means for detecting an optical power of a semiconductor laser, and a laser current for supplying an on / off current to the semiconductor laser. Driving means, first optical power setting means for setting a target peak optical power, comparing the first optical power detecting means and the first optical power setting means, and detecting the first optical power First feedback means for controlling the output on current of the laser current driving means so that the output of the means is equal to the first optical power setting means, and second light power setting for setting a target average optical power. Means, a second light power detection means for detecting the average light power of the semiconductor laser, and an error detector for detecting a voltage error between the second light power setting means and the second light power detection means A laser comprising: differential amplifying means for detecting a difference voltage between an external image signal and an output voltage of an error detector; and a second feedback means for feeding back the output of the differential amplifying means to the laser current driving means. In the driving device, a mode for receiving a clock signal of a predetermined period as the image signal is provided, and the error detector outputs the second optical power detecting means when the clock signal is input to the second optical power setting means. The error detector operates so as to be equal to the output, and the error detector has a function of holding an output voltage of the error detector when the clock signal is input.

[Operation] According to the above configuration of the present invention, the amount of laser light when the laser current is turned on is detected, and the laser peak current is set so that the detected value becomes a predetermined value. Since the average laser light amount when ON / OFF is detected and the detected slice level of the laser drive pulse is adjusted so that the detected value becomes a predetermined value,
Irrespective of the semiconductor laser characteristics and the high-frequency characteristics of the drive circuit for driving the laser current, it is possible to always obtain an accurate laser light quantity output of the laser light duty ratio and the peak value of the laser light quantity.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 is a block diagram of a semiconductor laser driving device, which best illustrates the features of the first embodiment of the present invention. In FIG.
The i terminal described as i1, i2, i3, etc. in each block indicates an input terminal. An o terminal described as o1 or the like indicates an output terminal.

In FIG. 1, reference numeral 1 denotes a semiconductor laser diode, and reference numeral 2 denotes a semiconductor laser diode. The semiconductor laser diode 2 detects a part of the laser light output from the semiconductor laser diode 1 and is substantially proportional to the laser light intensity. This is a PIN photodiode that converts current. Reference numeral 5 denotes a current-to-voltage converter for converting a current flowing through the photodiode 2 into a voltage, and reference numeral 8 denotes a low-pass filter connected to the output of the current-to-voltage converter 5 for detecting a low-frequency DC component of the voltage output from the current-to-voltage converter 5. Alternatively, it is an integrating circuit.

Reference numeral 3 denotes a high-speed current switch which is connected to the laser diode 1 and allows a current to be turned on / off to the laser diode 1. The high-speed current switch 3 has an ON / O for turning on / off the laser current.
There is an FF control terminal i ₁ and a current control terminal i ₂ for determining a laser current at the time of ON. I2 terminal of the high-speed current switch 3 is connected to the output o ₁ terminal of the voltage-current converter 4. The input terminal i ₁ of the voltage-current converter 4 is a sample-and-hold circuit 1
It is connected to the output terminal o ₁ of 4. The voltage-current converter 4 inputs a current proportional to the input voltage to the high-speed current switch 3, and the laser diode 1 is turned on / off by the high-speed current switch 3 at the current value. The input terminal i ₁ of the high-speed current switch 3 is connected to the output of the high-speed OR gate 11.

On the other hand, the output of the low-pass filter 8 is input to the inverting terminals of the differential amplifier 6 and the differential amplifier 10. The differential amplifier 6 amplifies a difference voltage between the voltage input from the low-pass filter 8 and the reference voltage 7. The voltage amplified by the differential amplifier 6 is applied to the input terminal i _{1 of the} sample and hold circuit 14.
And the sampled and held value of the output voltage of the differential amplifier 6 is input to the input terminal i ₁ of the voltage-current converter 4 via the o ₁ terminal of the sample and hold circuit 14.

The voltage input to the differential amplifier 10 amplifies a difference voltage from the reference voltage 9. The voltage amplified by the differential amplifier 10 is input to the input terminal i ₁ of the sample and hold circuit 13, and the sampled and held value of the output voltage of the differential amplifier 10 is output via the o ₁ terminal of the sample and hold circuit 13 at high speed. The signal is input to the non-inverting input terminal of the differential amplifier 12. The high-speed differential amplifier 12 operates as a high-speed comparator. A video signal composed of an ON / OFF pulse train including a predetermined rise time and fall time is input to the inverting terminal of the high-speed differential amplifier 12. With the non-inverting terminal of the high-speed differential amplifier 12 as a reference slice level, when the video signal level of the high-speed differential amplifier 12 is higher than the slice level, the output of the high-speed differential amplifier 12 is set to low level, When the level of the video signal of the dynamic amplifier 12 is lower than the slice level, a high-level voltage is output. The output of the high-speed differential amplifier 12 is input to the high-speed OR gate 11.

FIG. 2 shows the internal circuit configuration of the sample and hold circuits 13 and 14 in FIG. This sample and hold circuit has three input terminals i ₁ , i ₂ , i ₃ and 1
There is an output terminal o ₁ of this. In FIG. 2, i ₁ is an analog input signal for sampling and holding, and i ₂ is a selection signal for sampling or holding the analog input signal i ₁ . When i ₂ is at high level, the analog switch 15 is turned ON state, the voltage with the voltage applied to the analog input signal i ₁ is transferred to the output o ₁ is charged in the capacitor 17. When the selection signal i ₂ is at a low level, the analog switch 15 is turned off,
The voltage applied to the analog input signal i ₁ is not transmitted to the output o ₁ , and the voltage already charged in the capacitor 17 is held at the output o ₁ . i ₃ is a reset input terminal for resetting the sample and hold circuit. When the reset input terminal i ₃ becomes high level, the FET 16 turns on and discharges the electric charge charged in the capacitor 17.

As explained above, there are two feedback loops in the circuit of FIG. First, the first loop is a high-speed current switch 3 → a laser diode 1 → a photodiode 2 → a current-voltage converter 5 → a low-pass filter circuit 8 → a differential amplifier 6 → a sample-and-hold circuit 14 → a voltage-current converter 4 → a high-speed current switch. 3 is a feedback loop connected in order. The second feedback loop is composed of a high-speed current switch 3 → a laser diode 1 →
Photodiode 2 → current-voltage converter 5 → low-pass filter circuit 8 → differential amplifier 10 → sample-and-hold circuit 1
This is a feedback loop in which 3 → the high-speed differential amplifier 12 → the high-speed OR gate 11 → the high-speed current switch 3

Here, the first feedback loop is provided to stabilize the laser light at a predetermined level when the laser diode 1 is turned on. The target light quantity is set by the reference voltage 7.

The second feedback loop is provided to stabilize the average light level of the laser emission when the laser diode 1 is turned on / off at a predetermined cycle. The ON / OFF average light level of the target is set by the reference voltage 9. Then, the voltage of the reference voltage 9 is set lower than the reference voltage 7. The operation will be described below with reference to timing diagrams 3 and 4.

In this embodiment, after the control in the first feedback loop is completed, the control in the second feedback loop is performed.

First, control of the first feedback loop will be described. In FIG. 3, (3-1) to (3-
The control up to 9) corresponds to the control of the feedback loop.

In (3-1), the forced laser ON signal is at a low level, the video signal is at a high level, the sample and hold signal 1 is at a low level, the discharge signal 1 is at a high level, the sample and hold signal 2 is at a low level, and the discharge signal. 2 is fixed at a high level. At this time, the outputs of the sample hold circuits 13 and 14 are fixed at a low level (close to zero). The outputs of the high-speed differential amplifier 12 and the high-speed OR gate 11 are also fixed at a low level. Therefore, the high-speed current switch 3
The state becomes the F state, and the laser diode 1 does not emit light. Further, the output current of the voltage-current converter 4 is also close to zero. Since the laser diode 1 does not emit light, the PIN diode 2
, Almost no current flows, and the outputs of the current-voltage converter 5 and the low-pass filter 8 are also close to zero. Since the inverting terminal voltages of the differential amplifier 6 and the differential amplifier 10 become sufficiently higher than the reference voltages 7 and 9 connected to the respective non-inverting terminals, the outputs of the differential amplifier 6 and the differential amplifier 10 are output from the amplifiers. Outputs a high voltage up to the saturation level.

Next, at (3-2), the discharge signal 1 becomes low level. In this state, only the discharge FET inside the sample hold circuit 14 is turned off, and the output voltage does not change.

Then, in (3-3), the forced laser ON signal changes from low to high. At this time, the high-speed current switch 33
Of the high-speed current switch 3 changes from the OFF state to the ON state. However, even in this case, since the output of the voltage-current converter 4 is close to zero, the laser diode 1 does not emit light.

At (3-4), the sample hold signal 1 changes from low to high. At this time, the sample and hold circuit 14
Changes from the hold state to the sample state, and the capacitor 17 inside the sample hold circuit 14 starts charging (3.
-5), the voltage of the output terminal o1 of the sample and hold circuit 14 gradually increases at a predetermined gradient. As the voltage increases, the output current of the voltage-current converter 4 also increases, and the current flowing through the laser diode 1 also increases. Laser diode 1
When the current exceeds the threshold current, the laser diode 1 starts emitting light (3-6). As the laser diode 1 emits light, the output of the differential amplifier 6 also gradually increases. It is assumed that the shut-off frequency of the low-pass filter 8 is set in a region sufficiently higher than those of the sample-hold circuits 13 and 14. However, the output of the low-pass filter 8 rises almost unchanged from the rise of the output of the current-voltage converter 5 (which is proportional to the amount of laser light). When the voltage of the output o1 of the low-pass filter 8 rises and reaches the reference voltage 7, the output voltage of the differential amplifier 6 sharply decreases. Then, the differential amplifier 6 acts as a so-called error amplifier, and stops the rise of the laser current via the differential amplifier 6 → the sample / hold circuit 14 → the voltage-current converter 4 → the high-speed current switch 3. That is, the differential amplifier 6 performs a feedback operation so that the output of the low-pass filter 8 becomes equal to the reference voltage 7.

Then, when the light quantity of the laser diode 1 becomes sufficiently stable, the sample-and-hold signal 1 is returned from high to low, and the sample-and-hold circuit 14 is held (3-8). Further, in (3-9), the forced laser ON signal is changed from high to low, and the forced laser lighting is terminated. Thus, the control in the first feedback loop is completed.

Next, the control in the second feedback loop is started. First, the discharge signal 2 is changed from high to low in (3-10). In this state, the discharge FE inside the sample and hold circuit 13
Only when T is turned off, its output voltage does not change.

Then, a high-speed clock pulse having a predetermined cycle is applied to the video signal (3-11). FIG. 4 shows the waveform of the clock pulse. Since the clock has a high frequency, the time required for rising and falling of the clock occupies a considerable amount of time for one cycle of the clock.
Even in this state, since the non-inverting terminal of the high-speed differential amplifier 12 is fixed to almost zero, the output of the high-speed differential amplifier 12 does not change.

Next, at (3-12), the sample hold signal 2 is changed from low level to high level.
At this time, the sample hold circuit 13 changes from the hold state to the sample state, and the output of the sample hold circuit 13 gradually increases from zero. And the high-speed differential amplifier 12
According to the video signal (high-speed clock pulse)
N / OFF.

At this time, since the output voltage of the sample and hold circuit 14 is held in the first feedback operation, the peak current of the ON / OFF current of the laser diode 1 is not different from the current in the first feedback operation. . That is, the ON / OFF operation is performed with the ON current set in the first feedback operation. At this time O
N / OFF laser light is irradiated on the photodiode 2,
The laser light is converted into a current, and further converted into a voltage value by the current-voltage converter 5. The ON / OFF pulse output from the current / voltage converter 5 is input to the low-pass filter 8 and converted into a signal of a low frequency component, and the voltage of the output o1 of the low-pass filter 8 gradually increases (3-13).

If the response speed of the photodiode 2 and the current-to-voltage converter 5 is sufficiently lower than the high-speed ON / OFF clock pulse, the function as the low-pass filter 8 can be replaced by the photodiode 2 and the current-to-voltage converter 5, Even without the filter 8, a low-frequency DC signal can be obtained.

When the voltage of the output o1 of the low-pass filter 8 rises and reaches the reference voltage 9, the output voltage of the differential amplifier 10 sharply decreases (3-14). The output of the differential amplifier 10 is transmitted to the non-inverting terminal of the high-speed differential amplifier 12 via the sample and hold circuit 13. The non-inverting terminal of the high-speed differential amplifier 12 operates as a slice level when the high-speed differential amplifier 12 performs a comparator operation.

FIG. 4 shows this state. High-speed differential amplifier 1
2 is low (SL3 in FIG. 4), the high period of the high-low cycle of the high-speed differential amplifier 12, the high-speed OR gate 11, and the output of the high-speed current switch 3 becomes short, and the laser diode 1 is turned on. The ON period of the / OFF waveform becomes shorter. On the other hand, when the voltage of the non-inverting terminal of the high-speed differential amplifier 12 is high (SL1 in FIG. 4), the low period in the high-low cycle of the high-speed differential amplifier 12, the high-speed OR gate 11, and the output of the high-speed current switch 3 becomes short. The ON / OFF waveform of the laser diode 1 has a longer ON period. Therefore, the differential amplifier 10 operates as a so-called error amplifier, and a sample-and-hold circuit is provided so that the voltage at the inverting terminal of the differential amplifier 10 (which is proportional to the average light amount of the ON / OFF laser) is lower than the reference voltage 9. 13, the slice level of the high-speed differential amplifier 12 is changed. In this way, the feedback control is performed so that the ON / OFF laser average light amount becomes a predetermined value.

Then, at (3-15), the sample and hold signal 2 changes from high to low, and the sample and hold circuit 13 enters the hold state. Then, at (3-16), the high-speed ON / OFF pulse is stopped.

In this state, the sample and hold circuit 14
The internal condenser 17 stores the peak light amount of the laser,
The capacitor 17 inside the sample hold circuit 13 stores the average light amount when the laser is turned on / off.

(3-16) After that, by inputting arbitrary data to the video signal line, a stable peak light quantity when the laser diode 1 is turned on and a stable average light quantity when the laser diode 1 is turned on / off are obtained. (That is, stable ON / OFF duty ratio of the laser diode 1)
To turn on / off the laser diode 1 in any pattern
Can be done.

(Second Embodiment) FIG. 5 is a view best showing the features of the second embodiment of the present invention, and is a block diagram of a semiconductor laser driving device. In FIG. 5, the i terminal described as i ₁ , i ₂ , i _3, etc. in each block indicates an input terminal. An o terminal described as o ₁ or the like indicates an output terminal.

The block diagram of the semiconductor laser driving device shown in FIG. 5 is different from that of the first embodiment in that the differential amplifiers 6, 1
0, and in place of the sample and hold circuits 13 and 14, FIG.
The microcontrollers of the digitizing means and the signal processing means are used.

In the first embodiment, the differential amplifiers 6, 10
And the reference voltages 7 and 9 to the non-inverting terminals thereof and the functions performed by the sample and hold circuits 13 and 14,
0,22,23,24. All other circuit blocks in FIG. 5 are the same as those in FIG. 1, and duplicate description will be omitted. However, each code 20, 22,
23 and 24 will be mainly described.

In FIG. 5, reference numeral 20 denotes a low-pass filter 8.
Is converted into digital data, and the converted digital data is passed to the microcontroller 24.
The microcontroller 24 includes, in addition to the microcomputer, a ROM containing a program sequence and fixed data, and a RAM for temporary storage. 24 supplies digital data to the DA converters 22 and 23 according to the data received from the microcontroller 20. The DA converter 22 converts the received data into an analog voltage and inputs the analog voltage to the voltage-current converter 4. DA converter 2
3 also converts the received data into an analog voltage and inputs it to the high-speed differential amplifier 12.

In the circuit of FIG. 5, there are two feedback loops as in the first embodiment. First, the first loop is a high-speed current switch 3 → laser diode 1 → photodiode 2 → current-voltage converter 5 → low-pass filter circuit 8 → AD converter 20 → microcontroller 24 →
This is a feedback loop in which the DA converter 22 → the voltage / current converter 4 → the high-speed current switch 3 is connected in this order. Also,
The second feedback loop is a high-speed current switch 3 → laser diode 1 → photodiode 2 → current-voltage converter 5 → low-pass filter circuit 8 → AD converter 20 → microcontroller 24 → DA converter 23 → high-speed differential amplifier 12 → This is a feedback loop in which the high-speed OR gate 11 is connected to the high-speed current switch 3 in this order.

The first feedback loop is provided to stabilize the laser light when the laser diode 1 is turned on to a predetermined level. The target light quantity is set by ROM data stored inside the microcontroller 24, and the fluctuation data is stored in the RAM. The second feedback loop is provided to stabilize the average light level of the laser emission when the laser diode 1 is turned on / off at a predetermined cycle. The average light amount of the target is also set by ROM data separately stored inside the microcontroller 24, and the fluctuation data is stored in the RAM.

In FIG. 5, as in the first embodiment, after the first feedback loop control is performed, the second feedback loop control is performed. The procedure is almost the same as that of the first embodiment.

First, the microcontroller 24 causes the DA converters 22 and 23 to input zero data. Then, the forced laser ON signal is set to high. Then, the microcontroller 24 first gradually increases the data to be supplied to the DA converter 22, and causes the laser diode 1 to emit light from a gradually lower light amount. At this time, the output data of the AD converter 20 has a value proportional to the amount of laser light. Then, while monitoring the output data of the AD converter 20, it is detected whether the laser light amount has reached a predetermined peak value.

The microcontroller 24 is the AD converter 2
When it is recognized that the laser light amount has reached the predetermined peak value while monitoring the output of 0, the increase of the data given to the DA converter 22 is stopped. Then, the microcontroller 24 holds the value.

Then, the forced laser ON signal is returned to the low level in the step (3-9) shown in FIG. In this way, the amount of laser light at the time of laser ON is stabilized.

Next, the process enters the second feedback loop control. First, as in the first embodiment, a high-speed ON / OFF clock pulse is applied to a video signal. DA converter 2
The data given to 3 is gradually increased from zero. At this time, the output voltage of the DA converter 23 gradually increases, the voltage of the non-inverting terminal of the high-speed differential amplifier 12 increases, and the slice level of the high-speed differential amplifier 12 increases. The ON / OFF duty ratio gradually changes while the laser diode 1 emits light at the peak light amount determined by the first feedback loop control. And the microcontroller 24
(This corresponds to the average light amount at the time of laser ON / OFF) gradually increases. Then, the microcontroller 24 detects whether the laser average light amount has reached a predetermined reference value while monitoring the output data of the AD converter 20.

The microcontroller 24 is the AD converter 2
When it is recognized that the laser average light amount has reached the predetermined reference value while monitoring the output of 0, the increase of the data supplied to the DA converter 23 is stopped. Then, the microcontroller 24 holds the value. And high-speed ON / OF
The F pulse stops.

In this state, the microprocessor 24 stores the peak light amount of the laser, outputs the stored data to the DA converter 22, stores the average light amount when the laser is turned on / off, and stores the stored data in the DA converter. This means that the data is output to the converter 23.

Thereafter, as in the first embodiment, by inputting arbitrary data to the video signal line, the laser
The stable peak light quantity at the time and the stable average light quantity at the time of laser ON / OFF (that is, stable laser ON / OFF).
(OFF duty ratio) to turn on the laser in any pattern
/ OFF.

(Third Embodiment) In a third embodiment of the present invention, a case will be described in which the laser drive circuit of the above-described semiconductor laser is used in a laser beam printer or a magneto-optical disk. In FIG. 6, reference numeral 107 denotes a semiconductor laser as a light emitting element, which is a light source for image exposure and is applied to the above-described semiconductor laser. Also,
Reference numeral 101 denotes a DC scanner motor on which a polygon mirror, which is a polyhedral mirror for reflecting and rotating the laser light emitted from the semiconductor laser 107 and scanning the laser light, is mounted. This DC scanner motor 101 is composed of two sets of coils, and COIL1 is for starting with a large torque.
COIL2 is for control with small torque. Reference numerals 102 and 103 denote imaging lenses (surface tilt correction, Fθ lens, etc.) for correcting laser light scanned from a polygon mirror in the scanner motor 101, and 104 denotes a laser at a writing position from the imaging lens. This is a horizontal synchronization detection mirror (BD mirror) that reflects light. Reference numeral 105 denotes a reflection mirror that reflects laser light for image formation from the imaging lens onto the photosensitive drum, reference numeral 106 denotes a photosensitive drum, and reference numeral 108 denotes a beam detector (BD sensor) that detects the laser light reflected from the horizontal synchronization detection mirror. Yes, it corresponds to the PIN photodiode described in the first and second embodiments. 113 is an A / D converter, and 114 is a CPU. 1
Reference numeral 15 denotes a motor driver capable of driving a maximum of two sets of motors by a command from the CPU.

Next, the operation of the laser beam printer having the above configuration will be described.

First, the sequence during the operation of the scanner motor will be described. Based on the initial setting program, the CPU 114 stores a predetermined amount in the capacitor of the sample and hold circuit of the first feedback loop and the second feedback loop, for example, or in the RAM of the microcontroller according to the sequence shown in FIG. Thereafter, while operating each feedback loop in accordance with the set amount, the CPU responds to an image input signal (not shown).
Reference numeral 114 turns on the DRV signal, causes the semiconductor laser unit 107 to emit laser light, and irradiates the polygon mirror 101 with laser light. Then, the motor driver 117 is turned on in order to rotate the scanner motor, and a current is supplied to the bootstrap COIL 1 to apply a pulse to activate the bootstrap COIL 1. Then, as soon as the status signal SUB-RDY signal for stopping the driving of the coil 1 in the activation area becomes active, the coil 1 is stopped and rotated by inertia.

Then, when shifting from the starting area to the control area, the status signal RDY from the scanner motor is enabled, and the "H" state is transmitted to the CPU. Immediately after the CPU senses, the motor driver 117 turns on the control COIL2 side to apply a pulse, stops the oscillation pulse of the bootstrap COIL1, stops the oscillating pulse of the bootstrap COIL1, supplies a weak current to perform braking, and converges. The print speed is controlled by stabilizing the rotation speed.

As described above, the semiconductor laser driving device is
Irrespective of the high frequency characteristics of the drive circuit that drives the laser current, it is possible to always obtain an accurate laser light quantity output of the laser light duty ratio and the peak value of the laser light quantity. It can be formed with high quality, and the recording paper transferred from the photosensitive drum 106
A high-density, high-quality image signal is formed.

Although the laser beam printer has been described in the above embodiment, it goes without saying that the present invention can be similarly applied to laser driving of a semiconductor laser at the time of recording an image on a magneto-optical disk or data.

[0062]

According to the present invention, the amount of laser light when the laser current is turned on is detected, the laser peak current is set so that the detected value becomes a predetermined value, and the laser current is turned on / off. The average laser light amount at the time is detected, and the detection slice level of the laser drive pulse is adjusted so that the detected value becomes a predetermined value. Therefore, the semiconductor laser characteristics and the high frequency characteristics of the drive circuit for driving the laser current are affected. Therefore, it is possible to always obtain an accurate laser light quantity output of the peak value of the laser light quantity and the laser emission duty ratio.

[Brief description of the drawings]

FIG. 1 is a diagram most representing the features of a first embodiment of the present invention, and is a block diagram of the first embodiment.

FIG. 2 is a diagram illustrating an internal circuit of a sample and hold circuit used in FIG.

FIG. 3 is a control timing chart of the first embodiment.

FIG. 4 is a diagram illustrating an operation of a high-speed differential amplifier and a corresponding laser light amount waveform.

FIG. 5 is a diagram most representing the features of the first embodiment of the present invention, and is a block diagram of the second embodiment.

FIG. 6 is a conceptual diagram of a laser printer according to a third embodiment of the present invention.

[Description of Signs] 1 semiconductor laser diode 2 PIN photodiode 3 high-speed current switch 4 voltage-current converter 5 current-voltage converter 6 differential amplifier 7 reference voltage 8 low-pass filter or integration circuit 9 reference voltage 10 differential amplifier 11 high-speed OR Gate 12 High-speed differential amplifier 13 Sample hold circuit 14 Sample hold circuit 15 Analog switch 16 FET 17 Capacitor 20 AD converter 22, 23 DA converter 24 Microcontroller

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tetsuo Kishida 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 5D119 AA23 BA01 BA04 DA01 FA05 HA03 HA45 KA02 5F073 BA06 BA07 EA13 EA14 GA03 GA04 GA12 GA24 GA38

Claims (5)

[Claims] 1. A laser driving apparatus for a semiconductor laser, comprising: first feedback means for stabilizing a light amount level of the semiconductor laser; and second feedback means for setting an average light power of the semiconductor laser to a predetermined value. And a value corresponding to the image signal is input in advance, the set amount of the light amount level is stored in the storage unit in the first feedback unit, and then the storage amount in the second feedback unit is stored. A laser driving device which stores a set amount of the average optical power and drives the semiconductor laser while operating each of the feedback means according to each set amount. 2. A first optical power detecting means for detecting an optical power of a semiconductor laser, a laser current driving means for supplying an on / off current to the semiconductor laser, and a first light for setting a target peak optical power. Power setting means, comparing the optical power of the first optical power detecting means with the optical power of the first optical power setting means, wherein the optical power of the first optical power detecting means is equal to the first optical power. First feedback means for controlling the output on-current of the laser current driving means so as to be equal to the optical power of the power setting means; second optical power setting means for setting a target average optical power; and the semiconductor laser A second optical power detecting means for detecting the average optical power of the second optical power setting means and an error detecting the voltage error between the average optical power of the second optical power setting means and the average optical power of the second optical power detecting means. A detector, a differential amplifier for detecting a difference voltage between an external image signal voltage and a voltage error of the error detector, and a second feedback for feeding back an output of the differential amplifier to the laser current driver. Means for receiving a clock signal having a predetermined period as said image signal, wherein said error detector outputs said second optical power detection means when said clock signal is input. A laser driving device which operates so as to be equal to an output of the second optical power setting means, and wherein the error detector has a function of holding an output voltage of the error detector when the clock signal is input. . 3. The laser driving device according to claim 2, wherein said second optical power detecting means comprises a low-pass filter circuit to which an output signal of said first optical power detecting means is inputted. Laser drive. 4. The laser driving device according to claim 2, wherein the error detector amplifies a difference voltage between an output of the second optical power setting unit and an output of the second optical power detection unit. A laser drive device comprising: a dynamic amplifier; and a sample and hold circuit that samples and holds an output voltage of the differential amplifier. 5. The laser driving device according to claim 2, wherein said second optical power setting means outputs digital data, and said error detector converts an output of said second optical power detecting means into digital data. An A / D converter for conversion, a microcontroller for comparing the output of the second optical power setting means with the output data of the A / D converter, and a D / A converter for converting data output from the microcontroller to an analog value. Wherein the microcontroller operates to make output data of the AD converter equal to output data of the second optical power setting means.