JPH0951138A - Semiconductor laser drive controller - Google Patents

Abstract

(57) [Summary] (Correction) [PROBLEMS] To provide a semiconductor laser drive device that is not affected by variations in temperature characteristics and characteristics between lots, has high printing accuracy, and can be driven at high speed. SOLUTION: An adder 2 which outputs an addition signal when given an input signal, a monitor signal, a differential signal, and a comparison signal, a differential circuit 1 of an image signal, and a level when an output of the adder 2 and a reference signal are inputted. A control amplifier 6 that outputs a voltage signal according to the difference, and this voltage signal is applied to contact A or contact B according to the control signal.
To a switch circuit SW1, an output transistor T1 which receives a voltage signal from a contact A of the switch circuit SW1 to generate a drive current, a laser diode LD which emits light by this drive current, and a photodiode PD which monitors this laser light. A switch control circuit 5 for outputting a control signal in accordance with the forced lighting signal, a holding circuit 3 for holding and outputting a voltage signal level when the forced lighting signal is at a predetermined level,
A comparison amplifier 4 is provided which compares the voltage signal from SW1 with the level of the holding circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive control device for a semiconductor laser.

[0002]

2. Description of the Related Art As a device using a semiconductor laser, there are a laser printer and a measuring instrument. FIG. 13 shows a schematic configuration of a drive control device for a semiconductor laser in a conventional laser printer.

The electric signal transferred from the scanner 101 is given to the laser driving section 102, and the semiconductor laser 10
4 drive is controlled. Thereby, the semiconductor laser 10
Laser light is irradiated onto the drum 103 from 4 to form an electrostatic latent image. Thereafter, a development image, a transfer process, and a fixing process are performed to form a copied image on the paper surface.

In many cases, the laser driving section 102 generally adopts a sample hold method. As shown in FIG. 14, a point P1 at the beginning of the line to a point P at the end of the line
When printing one line up to 2, the irradiation of the laser light of the semiconductor laser 104 is turned on / off from the point P1 to the point P2 in the direction shown by the arrow A1. As a result, the drum 103 is irradiated with the laser beam in the hatched area, and an electrostatic latent image is formed.

When the point P2 is reached, it is necessary to keep the bias of the semiconductor laser 104 at this point to keep the characteristics of the semiconductor laser 104 constant over all rows. Therefore, the light emitted from the semiconductor laser 104 is received by the photodiode to start the closed loop control, and this control is applied from the point P2 at the end of a row to the point P1 at the beginning of the next row. . Point P
When it reaches 1, the closed loop control is stopped, the driving of the semiconductor laser is started, and the laser beam of the next row is irradiated.

By the way, there is a relationship as shown in FIG. 15 between the drive current supplied to the semiconductor laser and the electric power for irradiating the laser light. When the drive current supplied to the semiconductor laser 104 reaches the threshold current Ith, the power sharply increases. The slope efficiency, which is the rate of increase of electric power with respect to the drive current, indicated by the line 110 varies with temperature, and there is variation among lots.

This variation or variation in slope efficiency causes variation in the laser drive waveform as shown in FIG. Even if the drive waveform at the predetermined temperature is as shown by the solid line SL1, the rise time tr or the fall time tf changes as shown by the dotted line DL1 when the temperature changes,
It will cause overshoot and undershoot. Moreover, the same phenomenon may occur when the lots are different. When the drive waveform of the semiconductor laser varies, the print quality and print accuracy are deteriorated as a result.

Further, conventionally, by using a sample hold method, the closed loop control is removed during the period when the semiconductor laser is driven, and the control is performed to keep the bias of the semiconductor laser during the period when the semiconductor laser is not driven. Since it was repeated repeatedly, there was also a problem that it lacked in high speed.

[0009]

As described above, the conventional semiconductor laser drive control device has the problems that the print quality varies and the high speed is not achieved.

In view of the above circumstances, the present invention provides a semiconductor laser drive control device which is excellent in printing accuracy and is capable of being driven at high speed without being affected by temperature characteristics of semiconductor lasers and variations in characteristics between lots. The purpose is to provide.

[0011]

A semiconductor laser driving device according to the present invention includes an adder that receives an image signal from the outside and further receives a monitor signal, a differential signal, and a comparison signal, adds them, and outputs an added signal. , The image signal is applied to perform a differentiation operation, and the differentiation circuit that outputs the differentiation signal to the adder, the addition signal output from the adder, and the reference signal supplied from the outside are input, and the addition signal and the reference A control amplifier that outputs a voltage signal according to the level difference from the signal, the voltage signal output by the control amplifier, and the control signal are input, and the voltage signal is output according to the control signal to the first output terminal and the second output terminal. A switch circuit for outputting to one of the output terminals and an input terminal for the first output terminal of the switch circuit are connected, a voltage signal is given through the switch circuit, and a drive current corresponding to this voltage signal is generated. Power circuit, a laser diode that outputs the laser light by being supplied with the drive current generated by the output circuit, a monitor circuit that receives the laser light output by the laser diode, and outputs a monitor signal to the adder, and an external Is supplied with a forced lighting signal from the switch control circuit that outputs a control signal to the switch circuit according to the forced lighting signal, and the voltage signal output from the forced lighting signal and the control amplifier are supplied, and the forced lighting signal is at a predetermined level. Is connected to the holding circuit that holds and outputs the level of the voltage signal at the time, the second output terminal of the switch circuit, and the output terminal of the holding circuit, and is output from the control amplifier and given through the switch circuit. And a comparison amplifier that compares the voltage signal held by the holding circuit with the level of the voltage signal held by the holding circuit and outputs the comparison signal to the adder.

Another semiconductor laser drive control device of the present invention is an adder that adds signals input from the first, second and third input terminals and outputs the added signals from an output terminal, and inputs an image signal. An external input terminal connected to the external input terminal via the first resistor via an external input terminal;
Between the second input terminal of the adder and the differentiating circuit connected in parallel with the first resistor, and the inverting input terminal is connected to the output terminal of the adder, and the reference signal is externally applied to the non-inverting input terminal. A control amplifier that receives an input control amplifier and a control signal, and connects the input terminal and either the first output terminal or the second output terminal in accordance with the control signal. A switch circuit having an input terminal connected to the output terminal of, a bipolar transistor having a base connected to the first output terminal of the switch circuit, one end of which is grounded through a second resistor, and the other end of the bipolar transistor. A laser diode, both ends of which are connected to the power supply voltage terminal, is connected between the power supply voltage terminal and the third input terminal of the adder, and a laser diode which receives the laser light output from the laser diode is received. Diode, a forced lighting signal from the outside, and a switch control circuit that outputs a control signal based on this forced lighting signal, the forced lighting signal, and the output signal from the output terminal of the control amplifier When the lighting signal reaches a predetermined level, a holding circuit that holds a signal at a level substantially equal to the output signal from the control amplifier and outputs the signal from the output terminal and a non-inverting input terminal to the second output terminal of the switch circuit are connected and held. A comparison amplifier having an inverting input terminal connected to the output terminal of the circuit; and a third resistor having both ends connected between the output terminal of the comparator and the third input terminal of the adder. I am trying.

When the forced lighting signal is input to the holding circuit, the holding circuit outputs a voltage controlled oscillator that outputs an oscillation signal having a frequency corresponding to the level of the forced lighting signal, and an oscillation signal output from the voltage controlled oscillator. Input to the clock terminal,
The first comparison signal is input to the data terminal, the first signal is output while the first comparison signal is at the first level, and the first comparison signal is output when the first comparison signal is not at the first level. A latch circuit for stopping the output of the signal, a delay circuit for delaying and outputting the oscillation signal output from the voltage controlled oscillator for a predetermined time, an output of the delay circuit and an output of the latch circuit are provided, and the latch circuit is the first circuit. The clock signal is output during the output of the signal of, and the count operation is performed when the clock signal is output from the logic gate, which stops the output of the clock signal when the latch circuit stops outputting the first signal. Circuit for starting a count signal and outputting a count signal, and a digital / analog converter for receiving a count signal output from the counter circuit and outputting a second signal having a level corresponding to the count signal When the level of the second signal output from the digital / analog converter, and may comprise a comparator for outputting a first comparison signal by comparing the level of the output terminal of the control amplifier.

[0014]

When the frequency band of the laser diode and / or the photodiode is low, the image signal passing through these elements has a large rise time and fall time, but it is differentiated by this differentiation circuit by providing a differentiation circuit. By adding a signal with an adder, it is possible to obtain a waveform that is almost the same as the image signal input from the outside, and forcibly turn on the output level when the control amplifier is off and no drive current is flowing to the laser diode. By holding the output level of the control amplifier at this time and making it approximately match with this, the output level can be stabilized while the control amplifier is off.

[0015]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a circuit configuration of a semiconductor laser drive control device in this embodiment. The conventional device employs the sample hold method as described above, and cannot drive the semiconductor laser at high speed. Therefore,
In this embodiment, an automatic power control circuit (hereinafter referred to as an APC control circuit) is applied. Therefore, before describing the present embodiment, the basic circuit configuration of the APC control circuit will be described with reference to FIG.

The reference signal Sref is input to the non-inverting input terminal of the control amplifier 6, and the output terminal of the adder 2 is connected to the inverting input terminal. An input signal Si (image signal / VD) is input to one input terminal of the adder 2 via a resistor R1.
ATA) is input. The output terminal of the photodiode PD is connected to the other input terminal of the adder 2, and the output signal Sm (monitor signal) of the photodiode PD is input. The input signal Si and the signal Sm are added by the adder 2, and the added value Si + Sm is added to the control amplifier 6
It is input to the inverting input terminal of. The output terminal of the control amplifier 6 is connected to the base of an npn-type transistor T1 which is an output transistor, the collector is connected to the output terminal of the laser diode LD, and the emitter is grounded via the resistor R2. The input terminal of the laser diode LD is connected to the power supply voltage Vcc terminal. The photodiode PD is provided at a fixed interval from the laser diode LD, receives the laser light emitted by the laser diode LD, outputs a signal Sm according to the amount of received light, and gives it to the adder 2.

According to the APC control circuit having such a configuration, the signal Si is inputted from the outside, and the laser diode LD can be driven by the control amplifier 6 and the output transistor T1. In addition, the photodiode PD
To monitor the emission power of the laser diode LD,
The monitor signal Sm and the input signal Si are automatically controlled so that they always match. Therefore, even if the characteristics of the laser diode LD fluctuate under the influence of temperature or the characteristics of the laser diode LD vary from lot to lot, the laser diode LD is made to match the result monitored by the photodiode PD. The drive current supplied to is automatically controlled.

However, in the circuit configuration shown in FIG.
The control characteristics are insufficient in the following points. (1) The frequency characteristic of the optical system is low, and it cannot be used for high-speed printer control. (2) The output level from the control amplification unit 6 is unstable, and the rise time and fall time of the drive current to be supplied to the laser diode LD fluctuates.

First, regarding item (1), in many cases such as laser printers and measuring instruments, the photodiode PD is built in together with the laser diode LD.
Photodiode PD built in such a device
Generally has a band of several tens of MHz. In contrast,
The frequency of the input signal Si is 50 MHz in a high-speed printer
It is so expensive. Moreover, in order to control the driving of the laser diode LD in the high speed printer, it is necessary to set the rising and falling times of the driving current to 3 ns or less. Here, in the APC control circuit, the rise time tr of the drive current of the laser diode LD and the frequency band f
The following equation (1) is established between the BW and BW.

Tr = 0.35 * (1 / fBW) (1) From the equation (1), the control band required for the APC control circuit is 100 MHz or more.

A control block obtained by simplifying the circuit shown in FIG. 2 is shown in FIG. In the control loop, the control amplifier 6 and
It includes three components, a laser diode LD and a photodiode PD. Therefore, even if the band of the control amplifier 6 is 100 MHz or more, if the band of the photodiode PD is low, the band of the entire control loop becomes low.

Therefore, in order to increase the bandwidth of the control loop, the following elements are added. As shown in FIG. 4, when the transfer function of the optical system element including the laser diode LD and the photodiode PD is g (x), g
A transfer function f (x) that satisfies the relationship of (x) + f (x) = 1 is added in parallel to the resistor R1. This allows
The output from the control amplification unit 6 is the transfer function g of the optical system element.
Even if the band is reduced by (x), the transfer function f
A necessary band can be secured by newly adding the constituent element having (x).

The problem of item (2) will be described below.
Generally, in the APC control circuit, the laser diode LD is driven in a state where the laser diode LD emits light, that is, in FIG.
Control is performed between levels exceeding the threshold current Ith shown in FIG. This is because when the control is performed between the state in which the drive current is 0 and the level exceeding the threshold current Ith in FIG. 15, the laser diode LD is controlled to be turned on / off over the nonlinear region and the linear region. This causes the control to become unstable and slow down.

Therefore, a circuit for controlling the driving of the laser diode LD at a level exceeding the threshold current Ith is
As shown in FIG. The switch SW1 is connected between the base of the output transistor T1 and the output terminal of the control amplifier 6. The connection state of the switch SW1 is switched by the control signal output from the switch control circuit 5. The switch control circuit 5 receives the input signal Si supplied from the input unit 41.
A control signal is output based on (image signal / VDATA). When the input signal Si is at the high level, the switch control circuit 5 turns on the switch SW1 and drives the laser diode LD by the output transistor T1. On the contrary, when the input signal Si is at the low level, the on / off control circuit 5 turns off the switch SW1 to stop the driving of the laser diode LD.

With this configuration, when the switch SW1 is turned off by the input signal Si, the output level of the control amplifier 6 becomes unstable, and as a result, the threshold current Ith of the laser diode LD and the variation in slope efficiency affect the drive. The rise and fall times of the current vary.

In order to prevent such a phenomenon, a closed loop for holding the output of the control amplifier 6 at a constant level is newly formed while the laser diode LD is off.

FIG. 6 shows a basic configuration of a closed loop which operates when the laser diode LD is turned off. First, a laser printer generally uses signals as shown in FIG. The image mask signal / ENBL is at the low level during the period for printing one line. During this period, the image signal / V
The laser diode LD emits light according to DATA, and printing is performed. Before the printing for one line is performed, the laser diode LD is forcibly made to emit light for a trial by using the forced lighting signal / LON. Therefore, the output level of the control amplifier 6 during the period in which such forced lighting is performed is held in the holding circuit 11. Then, when the drive current of the laser diode LD is off, the bias voltage held in the holding circuit 11 is input to the inverting input terminal of the voltage comparison amplifier 4 as a reference voltage, and the non-inverting input terminal from the control amplifier 6 is input. Input the output of. From the voltage comparison amplifier 4, the result of comparing these two inputs is input to the inverting input terminal of the control amplifier 6 via the resistor R3. As a result, the output level of the control amplifier 6 matches the bias level held by the holding circuit 4. As a result, even if the characteristics of the laser diode LD fluctuate, the output level of the control amplification unit 6 becomes stable, and the rise time and fall time of the drive current flowing through the laser diode LD are kept constant.

The circuit shown in FIG. 7 corresponds to the circuit shown in FIG.
This corresponds to the PC control circuit to which the circuit for holding the bias level at the time of forced lighting is added. The APC control circuit in this embodiment shown in FIG. 1 is obtained by adding the differentiating circuit 1 represented by the transfer function f (x) shown in FIG. 4 in parallel to the resistor R1 to the circuit of FIG. Is.

Adder 2 and an input terminal to which an input signal is input
The resistor R1 and the differentiating circuit 1 are connected in parallel with one of the input terminals, and the output terminal of the adder 2 is connected to the inverting input terminal of the control amplifier 6. One end of the switch SW1 is connected to the output terminal of the control amplifier 6, and the contact A
Is connected to the base of the output transistor T1, and the contact B is connected to the non-inverting input terminal of the voltage comparison amplifier 4.

The output terminal of the laser diode LD is connected to the collector of the output transistor T1, and the input terminal of the laser diode LD and the input terminal of the photodiode PD are connected to the power supply voltage Vcc terminal. The output terminal of the photodiode PD is connected to the other input terminal of the adder 2.

Further, a switch control circuit 5 for controlling the switch SW1 is provided, and an input signal Si (forced lighting signal / LO) is provided to an input terminal of the switch control circuit 5.
The external input terminal to which N) is input is connected. One input terminal of the holding circuit 3 is connected to the output terminal of the control amplification unit 6, the other input terminal is connected to an external input terminal to which the input signal Si is input, and the output terminal is connected to the voltage comparison amplifier 4 The inverting input terminal of is connected. The output terminal of the voltage comparison amplifier 4 is connected to the input terminal of the adder 2 together with the output terminal of the photodiode PD via the resistor R3.

The operation of this embodiment having such a configuration is as follows. In the forced lighting time before starting printing, the low level forced lighting signal / LON is input to the holding circuit 3, and the holding circuit 3 starts the holding operation. As will be described later, the holding circuit 3 is given the output of the control amplification unit 6 during the forced lighting time, holds this output level even after the forced lighting ends, and inputs it to the non-inverting input terminal of the voltage comparison amplifier 4. Further, while the laser diode LD is off, the switch SW1 connects the output terminal of the control amplifier 6 and the contact B under the control of the switch control circuit 5. As a result, the voltage comparison amplifier 4 receives the output from the holding circuit 3 and the output from the control amplifier 6, and feeds back the result of comparison between the two to the adder 2. As a result, the output level of the control operational amplifier 6 when the laser diode LD is off is raised to the output level of the control amplifier 6 held by the holding circuit 3 at the time of forced lighting. Will be controlled to keep.

Next, in the print start period, the switch SW1 connects the output terminal of the control amplifier 6 and the contact A under the control of the switch control circuit 5. As a result, a drive current corresponding to the input signal Si (image signal / VDATA) is supplied to the laser diode LD to emit light.

Further, according to the present embodiment, since the differentiating circuit 1 is added, the frequency band of the optical system elements of the laser diode LD and the photodiode PD is low.
It is possible to prevent the band of the entire PC control circuit from being deteriorated.
FIG. 9 is simplified using the low-pass filter characteristic (LPF) 11 of the photodiode PD, the feedback efficiency (Km) 12 of the photodiode PD, and the slope efficiency (Kl) 13 of the laser diode LD in this embodiment. FIG. When the input signal Si (image signal / VDATA) having the drive waveform as shown in FIG. 9A is input, it is output from the photodiode PD due to the influence of the low-pass filter characteristic 11 of the photodiode PD. The monitor signal Sm has a slow rising waveform as shown in FIG. On the other hand, the differential circuit 1 connected in parallel to the resistor R1 outputs a signal Sc having a differential waveform as shown in FIG. 9 (b), which is input to the adder 2 together with the monitor signal Sm. As a result,
The signal Sc + Sm having a waveform as shown in FIG. 9D is output from the adder 2, and it is possible to obtain a characteristic almost equal to that of the input signal Si.

FIG. 12 shows the result of simulation of the waveform of the drive signal of the laser diode LD obtained in this embodiment. Here, as setting conditions, the frequency of the input signal Si (image signal / VDATA) is 20 MHz,
The frequency band of the laser diode LD was 5 MHz.
According to this simulation, the rise time is about 2.1 nsec and the fall time is about 1.7 ns.
ec. As described above, according to this embodiment, it is possible to generate a good drive waveform even if the band of the optical system element is low.

FIG. 10 shows an example of a specific configuration of the holding circuit 3. This circuit is analog / digital (A / D)
It is composed of a conversion circuit and a digital / analog (D / A) conversion circuit. D-type flip-flop (hereinafter referred to as DF
Power supply voltage Vcc to the data output terminal D of 51)
The terminals are connected and the forced lighting signal LON is input to the clock terminal. Voltage controlled oscillator (hereinafter referred to as VCO) 5
The forced lighting signal LON is input to the second input terminal, and the output terminal is connected to the input terminal of the inverter train including the inverters 53 to 56 connected in series. D-FF51
The reset terminal R of the output terminal of the VCO 52 and DF
It is connected to the clock terminal of F58. D-FF58
Data output terminal Q and the inverter array output terminal are NO
NOR gate connected to each of the two input terminals of the R gate 57
The output terminal of the gate 57 is DF which constitutes an octal counter.
It is connected to the clock terminal of the D-FF 71 out of F71 to 78. The reset terminals R of the D-FF 71 to D-FF 78 are commonly connected to the data output terminal Q of the D-FF 51. In the D-FFs 71 to 78, the data terminal Q at the previous stage is connected to the clock terminal at the next stage and the digital / analog circuit (hereinafter referred to as the D / A circuit) 63. Data inversion output terminal / Q of each D-FF 71-78
Are connected to their respective data input terminals D and D / A circuits 63.

The output terminal of the D / A circuit 63 is a comparison circuit 64.
Is connected to one input terminal, the other terminal of the comparison circuit 64 is connected to the output terminal of the control amplifier 6, and the output terminal of the comparison circuit 64 is connected to the data input terminal D of the D-FF 58. .

FIG. 11A shows the forced lighting signals LON and D.
-Output signal Re of FF51, output signal CL of VCO52
K00, NOR gate 57 output signals CLK0, DF
Output signals CLK1 to F71 to 78 from the data terminals Q
A time chart of CLK8 is shown in FIG.
The waveform of the output signal of the A circuit 63 is shown.

When the forced lighting signal LON rises to a high level, this signal is input to the D-FF 51 and VCO 52. A high-level signal Re is output from the data terminal Q of the D-FF 51, input to the reset terminals R of the D-FFs 71 to 78, and all are reset. Also, VCO5
2 starts oscillating operation and outputs a signal having a frequency corresponding to the level of the forced lighting signal LON. The VCO 52 operates only while the forced lighting signal LON is at a high level, and stops operating when it falls to a low level.

When the VCO 52 operates and outputs a signal, this signal is input to the reset terminal R of the D-FF 51 and reset, and the low level signal Re from the data terminal D.
Is input to the reset terminals R of the D-FFs 71 to 78, and the reset state is released.

The output of the VCO 52 is input to the clock terminal of the D-FF 58, the signal output from the output terminal Q, and
The output signal of the VCO 52 delayed by the inverter train is input to the NOR 57 and the clock signal CLK.
0 is generated, and the first stage D-FF71 of the octal counter
It is given to the clock terminal of. From the data output terminals Q of the D-FFs 71 to 78, the clock signal CLK1 is output.
8 to 8 are output and given to the D / A circuit 63. The clock signals CLK1 to CLK8 correspond to the count data of the least significant bit to the most significant bit in order.

The output level of the D / A circuit 63 is shown in FIG.
It changes as shown in FIG. When the octal counter starts counting, an analog amount output corresponding to the count value is output from the D / A circuit 63 to the comparison circuit 64. D
The output level of the / A circuit 63 gradually increases as shown by the solid line 22. The comparison circuit 64 includes the control amplifier 6
Output level of the D / A circuit 63 is compared with the output level of the D / A circuit 63, and the high level output is DF until the output level of the D / A circuit 63 reaches the output level of the control amplifier 6.
It is given to the data terminal D of F58. This allows the D-FF
A high level output is applied to one input terminal of the NOR gate 57 from the output terminal Q of the NOR gate 57.
Will continue to output the clock signal CLK0.

As indicated by the solid line 22, the D / A circuit 6
When the output level of 3 reaches the output level of the control amplifier 6, the output of the comparison circuit 64 becomes low level, and the D-FF
A low level signal is output from the output terminal Q of 58. As a result, the clock signal CLK0 is not output from the NOR gate 57, and the counting operation of the octal counter is also stopped. D / A indicated by the solid line 22 at this time
The output level of the circuit 63 is held and given to the comparison amplifier 4.

As described above, according to the holding circuit of FIG.
When the forced lighting signal LON rises to the high level, the VCO
The oscillating operation of 52 starts, the count operation of the octal counter starts, and the analog quantity corresponding to this count value is D /
When the output level is output from the A circuit 63 and this output level matches the output level of the control amplifier 6 at the time of forced lighting, the level at this time is held even after the forced lighting. As a result, the output level of the control amplifier 6 when the forced lighting signal LON is at the high level can be retained even after the operation of the control amplifier 6 is stopped. As a result, the rise time and the fall time of the drive waveform can be made constant without being affected by the temperature characteristics of the optical system element and the variations in characteristics between lots, and the printing quality and accuracy are improved.

The above-described embodiments are merely examples and do not limit the present invention. For example, although the present embodiment is applied to the laser printer, the present invention is not limited to the laser printer and can be similarly applied to control of driving of a semiconductor laser widely used in measuring instruments and the like. The circuit configuration of the holding circuit is not limited to that shown in FIG. 10 and may be any circuit that can hold the output level of the control amplifier during forced lighting.

[0047]

As described above, the semiconductor laser drive control device of the present invention inputs from the outside by adding the signal obtained by differentiating the image signal by the differentiating circuit to the signal passing through the optical system element having a low frequency band. It is possible to obtain a drive waveform that is almost the same as the generated image signal, and to maintain the output level of the control amplifier during forced lighting to stabilize the output of the control amplifier when it is turned off. It is possible to make the rising and falling characteristics of the drive waveform constant without being affected by the characteristics or the variation between lots.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a semiconductor laser drive control device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a semiconductor laser drive control device to which an APC control circuit is applied.

FIG. 3 is a block diagram showing control blocks of the semiconductor laser drive control device shown in FIG.

4 is a circuit diagram showing a configuration in which a differentiating circuit is added to the semiconductor laser drive control device shown in FIG.

5 is a circuit diagram showing a configuration in which a switch and a switch control circuit are added to the output terminal of the control amplifier of the semiconductor laser drive control device shown in FIG.

6 is a circuit diagram showing a configuration in which a holding circuit for holding the output level of the control amplifier of the semiconductor laser drive control device shown in FIG. 2 is added.

FIG. 7 is a circuit diagram showing a configuration of a semiconductor laser drive control device in which the circuits shown in FIGS. 5 and 6 are combined.

FIG. 8 is a time chart showing the waveform of each signal used in the semiconductor laser drive control device of this embodiment.

FIG. 9 is a diagram showing an image signal input to the semiconductor laser drive control device, a signal Sm output via an optical system element, a signal Sc differentiated by a differentiating circuit, a signal Sm and a signal Sc.
The time chart which showed the signal which added and.

FIG. 10 is a circuit configuration diagram showing a specific example of a holding circuit in the semiconductor laser drive control device.

FIG. 11 is a time chart showing waveforms of respective signals in the semiconductor laser drive control device.

FIG. 12 is a time chart showing a result obtained by simulating a waveform of a drive current generated by the semiconductor laser drive control device.

FIG. 13 is an explanatory diagram showing the basic principle of driving a semiconductor laser diode in a laser printer.

FIG. 14 is an explanatory diagram showing waveforms of signals for driving the semiconductor laser diode.

FIG. 15 is an explanatory diagram showing a relationship between a drive current and power of the semiconductor laser diode.

FIG. 16 is an explanatory diagram showing a waveform of a drive current of the semiconductor laser diode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Differentiation circuit 2 Adder 3 Holding circuit 4 Comparison amplifier 5 Switch control circuit 6 Control amplifier 11 Low pass filter characteristic 12 Feedback efficiency 13 Slope efficiency 51, 58, 71-78 D-FF 52 Voltage control oscillator 53-56 Inverter 57 NOR gate 63 D / A circuit 64 Comparison circuit T1 npn transistor LD laser diode PD photodiode R1, R2, R3 resistance Si input signal Sref reference signal / VDATA image signal / ENBL image mask signal / LON forced lighting signal

Claims (3)

[Claims] 1. An adder which receives an image signal from the outside, further adds a monitor signal, a differential signal, and a comparison signal, which will be described later, and outputs the added signal; and the image signal. A differential circuit that performs a differential operation to output the differential signal to the adder, the addition signal output from the adder, and a reference signal provided from the outside, and the addition signal and the reference A control amplifier that outputs a voltage signal according to a level difference from a signal, the voltage signal output by the control amplifier, and a control signal described below are input, and the voltage signal outputs a first output according to the control signal. A switch circuit that outputs to one of a terminal and a second output terminal; an input terminal connected to the first output terminal of the switch circuit; and a voltage signal supplied through the switch circuit. An output circuit that generates a drive current according to the voltage signal of the laser diode, a laser diode that is supplied with the drive current generated by the output circuit and outputs a laser beam, and that receives the laser beam output by the laser diode. A monitor circuit that outputs the monitor signal to the adder; a switch control circuit that receives a forced lighting signal from the outside and outputs the control signal to the switch circuit according to the forced lighting signal; And a voltage signal output from the control amplifier, and a holding circuit that holds and outputs the level of the voltage signal when the forced lighting signal is at a predetermined level; and a second output terminal of the switch circuit. And a voltage signal that is connected to the output terminal of the holding circuit and that is output from the control amplifier and given through the switch circuit, Comparing the level of said voltage signal whose serial holding circuit is held, the semiconductor laser drive control device, characterized in that said comparison signal and a comparator amplifier output to the adder. 2. An adder for adding signals input from first, second and third input terminals and outputting from an output terminal, wherein a first resistor is provided at an external input terminal to which an image signal is input. A differential connected in parallel with the first resistor between the adder to which the first input terminal is connected via, the external input terminal, and the second input terminal of the adder. A circuit, a control amplifier having an inverting input terminal connected to the output terminal of the adder, and a reference signal input from the outside to a non-inverting input terminal; and a control signal described later, which is input terminal according to the control signal. A switch circuit for electrically connecting one of the first output terminal and the second output terminal, the switch circuit having the input terminal connected to the output terminal of the control amplifier; Connect the base to the first output terminal A bipolar transistor whose one end is grounded via a second resistor, a laser diode whose both ends are connected between the other end of the bipolar transistor and a power supply voltage terminal, the power supply voltage terminal and the adder. And a photodiode for receiving the laser light output from the laser diode, and a forced lighting signal from the outside, and the control signal is transmitted based on the forced lighting signal. A switch control circuit for outputting, the forced lighting signal, and an output signal from the output terminal of the control amplifier are input, and when the forced lighting signal reaches a predetermined level, a signal having a level substantially equal to the output signal from the control amplifier. And a non-inverting input terminal connected to the second output terminal of the switch circuit, A comparator amplifier having an inverting input terminal connected to the output terminal of the holding circuit; and a third resistor having both ends connected between the output terminal of the comparator and the third input terminal of the adder. A semiconductor laser drive control device characterized by the above. 3. The voltage holding oscillator, which outputs an oscillation signal having a frequency corresponding to the level of the forced lighting signal when the holding circuit receives the forced lighting signal, and the output circuit of the voltage controlled oscillator. The oscillation signal is input to the clock terminal, the later-described first comparison signal is input to the data terminal, and the first comparison signal is output while the first comparison signal is at the first level. Is not at a first level, a latch circuit that stops outputting the first signal, a delay circuit that delays the oscillation signal output from the voltage controlled oscillator by a predetermined time, and outputs the delayed signal, and an output of the delay circuit And an output of the latch circuit, the clock signal is output while the latch circuit is outputting the first signal, and the first latch circuit stops outputting the first signal. The black A logic gate for stopping the output of a clock signal, a counter circuit for starting a counting operation and outputting a count signal when the clock signal is output from the logic gate, and a counter circuit for providing the count signal output from the counter circuit The second level having a level corresponding to this count signal
A digital / analog converter that outputs a signal of the second, and the second output from the digital / analog converter.
3. The semiconductor laser drive control according to claim 1 or 2, further comprising: a comparator that compares the level of the signal of 1) with the level of the output terminal of the control amplifier to output the first comparison signal. apparatus.