JP5304235B2 - Semiconductor laser array light quantity control circuit and image forming apparatus using the semiconductor laser array light quantity control circuit - Google Patents

Description

  The present invention relates to a semiconductor laser drive circuit used in an image forming apparatus, and more particularly to a semiconductor laser array light amount control circuit for detecting the light amounts of a plurality of semiconductor lasers with a photodiode and controlling them to a predetermined light amount.

Semiconductor lasers are widely used in the fields of printers, optical disks, optical communications, and the like because they are small and inexpensive and can easily obtain laser light simply by flowing current.
However, since the current-light quantity characteristic has temperature dependence, special light quantity control is necessary to obtain a constant light quantity. This light quantity control is called APC (Automatic Power Control).
Prior to the actual driving of the semiconductor laser, the APC drives the semiconductor laser, receives the amount of light emitted by the photodiode, and stores the current value at which the output of the photodiode reaches a predetermined level in the storage means. Thus, control is performed so as to obtain a stable light emission amount.

  In recent years, with an increase in writing speed, there have been an increasing number of systems in which a plurality of semiconductor lasers are arranged in an array and the semiconductor lasers are driven simultaneously. Such a semiconductor laser array incorporates photodiodes for APC, but the number of photodiodes may be smaller than the number of semiconductor lasers, and there is one. Thus, in order to perform APC when there is one photodiode, it was necessary to drive the semiconductor lasers one by one and perform APC. As such a technique, for example, as a first method, when APC is performed on an arbitrary semiconductor laser in a semiconductor laser array, a drive circuit of another semiconductor laser has a low level (white A data signal that produces a light emission output of level) is input (see, for example, Patent Document 1).

When driving a semiconductor laser, two normal control currents are used. One is a bias current close to the threshold current of the semiconductor laser, and the other is a switching current that causes the semiconductor laser to emit light with a predetermined amount of light.
The semiconductor laser has a threshold current at which light emission starts, and the semiconductor laser hardly emits light until the supplied current reaches the threshold current. When driving a semiconductor laser, even if the drive current is suddenly increased from 0 A to the light emission current, light emission does not start until the light emission current reaches the threshold current. . For this reason, usually, a method has been employed in which a bias current close to the threshold current is given to the semiconductor laser, and when actually emitting light, a switching current is added to the bias current. In the first method, when APC is performed, the switching current is set to 0 A and the light quantity of the semiconductor laser is set to the white level except for the semiconductor laser that is the target of APC.
JP 2002-178559 A

  However, when the number of semiconductor lasers is increased, there is a problem that even a slight light emission with a bias current is added to adversely affect APC. Further, when the output of one photodiode is input to many drive circuits, there is a problem that the input impedance of the photodiode input circuit is lowered and the detection accuracy is lowered. In order to prevent such a decrease in input impedance, a special circuit is sometimes added between the photodiode and the drive circuit.

  The present invention has been made to solve such problems, and a semiconductor laser array light amount control circuit capable of performing high-precision APC even when the number of semiconductor lasers increases, and the semiconductor laser array light amount. It is an object to obtain an image forming apparatus using a control circuit.

A semiconductor laser array light amount control circuit according to the present invention is a semiconductor laser array light amount control circuit for controlling the light amount of a semiconductor laser array having a plurality of semiconductor lasers.
A light receiving element for receiving the amount of light output from each of the semiconductor lasers;
In response to the input automatic light amount control signal, each automatic light amount control circuit that performs control to set the light emission amount output from the corresponding semiconductor laser to a predetermined light emission amount according to the output of the light receiving element;
With
Each of the automatic light quantity control circuits inputs the automatic light quantity control signal input to itself to the other automatic light quantity control circuit, thereby prohibiting the operation of the other automatic light quantity control circuit and corresponding the semiconductor laser. While the automatic light quantity control is performed in accordance with the automatic light quantity control signal input by one of the automatic light quantity control circuits, the other automatic light quantity control circuits operate so as to cut off the current supply to Is stopped and the current supply to the corresponding semiconductor laser is cut off.

Specifically, each of the automatic light quantity control circuits is
A first light amount control input terminal to which the automatic light amount control signal for performing the automatic light amount control is input to the corresponding semiconductor laser;
One or more second light quantity control input terminals for inputting the automatic light quantity control signal to the other automatic light quantity control circuits;
With
When the automatic light amount control signal is input to any one of the second light amount control input terminals, the operation is stopped and the current supply to the corresponding semiconductor laser is cut off.

  Each of the automatic light quantity control circuits inputs the automatic light quantity control signal input to the first light quantity control input terminal to the second light quantity control input terminal of the other automatic light quantity control circuit. The operation of other automatic light quantity control circuits is prohibited, and the current supply to the corresponding semiconductor laser is cut off.

  Each automatic light amount control circuit includes a photocurrent input terminal to which a photocurrent output from the light receiving element is input, and while the other automatic light amount control circuits are operating, the photocurrent The photocurrent to the input terminal is cut off so that the photocurrent input terminal is in a high impedance state.

A plurality of semiconductor devices having a plurality of automatic light quantity control circuits;
Each of the semiconductor devices is
Each first light amount control input terminal to which each of the automatic light amount control signals for operating each of the built-in automatic light amount control circuits is input correspondingly;
Each second light quantity control input terminal to which the respective automatic light quantity control signals for operating the respective automatic light quantity control circuits in the other semiconductor devices are input correspondingly;
With
While the automatic light quantity control signal is inputted to one of the semiconductor devices and the automatic light quantity control is performed, the operation of the other automatic light quantity control circuits built in and the respective automatic light quantity control circuits built in the other semiconductor devices are performed. The current supply to all the semiconductor lasers connected to the automatic light quantity control circuit that prohibited the operation was blocked.

  In this case, each of the semiconductor devices prohibits the operation of all of the built-in automatic light quantity control circuits when the automatic light quantity control signal is input to any of the second light quantity control input terminals. All the current supply to each semiconductor laser connected corresponding to each automatic light quantity control circuit was cut off.

  Each of the automatic light quantity control circuits can input the automatic light quantity control signal input to the first light quantity control input terminal to the second light quantity control input terminal of the other automatic light quantity control circuit. The operation of the automatic light quantity control circuit is prohibited, and all the current supply to the corresponding semiconductor laser is cut off.

  Each of the semiconductor devices includes a photocurrent input terminal to which a photocurrent output from the light receiving element is input, and while the automatic light quantity control circuit in the other semiconductor device is operating, The photocurrent to the photocurrent input terminal is interrupted to place the photocurrent input terminal in a high impedance state.

  Each of the semiconductor devices includes an internal automatic light quantity control signal generation circuit that generates an internal automatic light quantity control signal by inputting the automatic light quantity control signal input to the plurality of first light quantity control input terminals, The internal automatic light amount control signal generation circuit is configured to generate one internal automatic light amount control signal according to a predetermined priority when a plurality of the automatic light amount control signals are simultaneously input.

  The internal automatic light quantity control signal generation circuit outputs the internal automatic light quantity control signal after a predetermined time has elapsed with respect to the automatic light quantity control signal.

  Further, the internal automatic light quantity control signal generation circuit, when a plurality of the automatic light quantity control signals are inputted at the same time, after the input of the automatic light quantity control signal having a high priority is finished, the predetermined time elapses. After that, the next internal automatic light amount control signal is output.

  Further, the internal automatic light quantity control signal generation circuit has turned off all of the automatic light quantity control signals of the other semiconductor devices from the state where the automatic light quantity control signals are simultaneously input to the semiconductor device and the other semiconductor devices. In this case, the internal automatic light amount control signal is output after a predetermined time has elapsed.

  Further, when the automatic light amount control signal is input simultaneously with other semiconductor devices, the semiconductor device prohibits the operation of all the built-in automatic light amount control circuits and supplies all current to the corresponding semiconductor laser. I tried to block it.

  An image forming apparatus according to the present invention includes any one of the semiconductor laser array light quantity control circuits described above.

  According to the semiconductor laser array light quantity control circuit of the present invention and the image forming apparatus having the semiconductor laser array light quantity control circuit, during the APC of one semiconductor laser, both the bias current and the switching current to the other semiconductor laser are completely supplied. As in the past, semiconductor lasers other than those in the APC are slightly turned on by the bias current, and the APC adjustment accuracy is not reduced by the minute light emission. In particular, when the number of semiconductor lasers is large, an error due to the slight lighting cannot be ignored, which is effective.

Further, when APC is not performed, the PD terminal for connecting the photodiode to the automatic light quantity control circuit is set in a high impedance state, so that a current mirror using a MOS transistor which has been necessary in the past is used. A circuit is not required and wired OR connection is possible, so that the number of external parts can be greatly reduced, and accordingly, downsizing and cost reduction can be achieved.
Furthermore, since a delay time is provided before APC is performed, even when APC is continuously performed, the next APC is not started until a predetermined time has elapsed after the previous APC is completed. APC mutual interference can be completely eliminated.

Next, the present invention will be described in detail based on the embodiments shown in the drawings.
First embodiment.
FIG. 1 is a diagram showing a circuit example of a semiconductor laser array light quantity control circuit according to the first embodiment of the present invention.
The semiconductor laser array light quantity control circuit of FIG. 1 is composed of two automatic light quantity control circuits 10 and 20, a semiconductor laser array 30, PMOS transistors M1 and M2, NMOS transistors M3 to M5, and adjustable resistors R1 and R2. Yes. Since the automatic light quantity control circuits 10 and 20 are exactly the same circuit, the internal circuit of the automatic light quantity control circuit 20 is omitted in FIG.

The automatic light quantity control circuit 10 includes an APC control circuit 11, a switching current generation circuit 12, a bias current generation circuit 13, an inverter circuit 14, AND circuits 15 and 17, an OR circuit 16, and switches SW11 and SW12, and an APC terminal, An LDOFF terminal, an RPD terminal, a PD terminal, an LD terminal, and a DATA terminal are provided. The APC terminal serves as a first light quantity control input terminal, the LDOFF terminal serves as a second light quantity control input terminal, and the PD terminal serves as a photocurrent input terminal.
The semiconductor laser array 30 includes two semiconductor lasers LD31 and LD32 and a photodiode PD31.

The automatic light amount control signal APC1 is input to the APC terminal of the automatic light amount control circuit 10 and the LDOFF terminal of the automatic light amount control circuit 20, respectively. The automatic light amount control signal APC2 is input to the LDOFF terminal of the automatic light amount control circuit 10 and automatic light amount control. Each is input to the APC terminal of the circuit 20.
A write signal of the semiconductor laser is input to the DATA terminal of the automatic light quantity control circuit 10, and one end of a resistor R1 that converts the photocurrent of the photodiode PD31 into a voltage is connected to the RPD terminal of the automatic light quantity control circuit 10. Yes. The other end of the resistor R1 is connected to the power supply terminal Vdd.

  The PD terminal of the automatic light quantity control circuit 10 is connected to the drain of the NMOS transistor M3, and the source of the NMOS transistor M3 is connected to the ground voltage GND. The gate of the NMOS transistor M3 is connected to the gates of the NMOS transistors M4 and M5 and to the drain of the NMOS transistor M4. Since the sources of the NMOS transistors M4 and M5 are respectively connected to the ground voltage GND, the NMOS transistors M3 to M5 form a current mirror circuit. The drain of the NMOS transistor M4 is connected to the drain of the PMOS transistor M1. In the PMOS transistor M1, the source is connected to the power supply voltage Vdd, and the gate is connected to the gate of the PMOS transistor M2 and to the drain of the PMOS transistor M2. Since the source of the PMOS transistor M2 is connected to the power supply voltage Vdd, the PMOS transistors M1 and M2 also form a current mirror circuit.

The drain of the PMOS transistor M2 is connected to the cathode of the photodiode PD31, and the drain of the NMOS transistor M5 is connected to the PD terminal of the automatic light quantity control circuit 20.
The anode of the semiconductor laser LD31 is connected to the LD terminal of the automatic light quantity control circuit 10, and the anode of the semiconductor laser LD32 is connected to the LD terminal of the automatic light quantity control circuit 20. The cathodes of the semiconductor lasers LD31 and LD32 and the anode of the photodiode PD31 are connected in common and connected to the ground voltage GND.
In the automatic light quantity control circuit 10, the input terminal of the inverter circuit 14 is connected to the LDOFF terminal, and the LDOFFB signal is output from the output terminal of the inverter circuit 14. In the AND circuit 15, the LDOFFB signal is input to the first input terminal, the second input terminal is connected to the APC terminal, and the output terminal is connected to the APC control circuit 11.

In the OR circuit 16, the first input terminal is connected to the APC terminal, the second input terminal is connected to the DATA terminal, and the output terminal is connected to the second input terminal of the AND circuit 17. In the AND circuit 17, the LDOFFB signal is input to the first input terminal, and the output terminal is connected to the control terminal of the switch SW11.
The APC control circuit 11 performs control so that the light emission amount of the semiconductor laser LD31 becomes a predetermined light amount in accordance with the automatic light amount control signal APC1, and stores the bias current and the switching current value for obtaining the light amount. Do.
In the APC control circuit 11, an input terminal is connected to the RPD terminal and the PD terminal, and an output terminal is connected to the switching current generation circuit 12 and the bias current generation circuit 13, respectively.

The bias current generation circuit 13 is a circuit that generates a bias current close to the threshold current of the semiconductor laser LD31, and one end of the switch SW12 is connected to the output end. The other end of the switch SW12 is connected to the LD terminal, and the LDOFFB signal is input to the control terminal of the switch SW12.
The switching current generation circuit 12 is a circuit that generates a switching current for the semiconductor laser LD31 to output a predetermined amount of light. The semiconductor laser LD31 outputs a predetermined amount of light by the sum current of the switching current and the bias current. To do. The output terminal of the switching current generation circuit 12 is connected to one end of the switch SW11, and the other end of the switch SW11 is connected to the LD terminal.

Next, the operation of the semiconductor laser array light quantity control circuit of FIG. 1 will be described.
When the automatic light quantity control signal APC2 is low level and the automatic light quantity control signal APC1 becomes high level, the automatic light quantity control circuit 10 starts the APC operation. Since the automatic light quantity control signal APC2 is at a low level, the LDOFF terminal is at a low level. The low level signal is inverted by the inverter circuit 14 to become a high level, and is output as an LDOFFB signal. When the LDOFFB signal becomes high level, the switch SW12 is turned on and the output terminal of the OR circuit 16 also becomes high level, so that the output signal of the AND circuit 17 also becomes high level and the switch SW11 is turned on. Further, the output signal of the AND circuit 15 also becomes high level, and the APC control circuit 11 is operated.

There are mainly the following three methods for APC.
The first method is to fix the switching current and adjust only the bias current, the second method is the method to fix the bias current and adjust only the switching current, and the third method In this method, both the bias current and the switching current are adjusted. The present invention can be applied to all three methods.
As described above, in the first embodiment, the output signal of the APC control circuit 11 is output to the switching current generation circuit 12 and the bias current generation circuit 13 respectively, but only the switching current is adjusted. The output signal from the APC control circuit 11 to the bias current generation circuit 13 is unnecessary. Similarly, when adjusting only the bias current, an output signal from the APC control circuit 11 to the switching current generation circuit 12 is unnecessary.

  When the APC adjustment of the semiconductor laser LD31 is performed, the APC1 signal is set to the high level when the APC2 signal is at the low level. Then, as described above, the switches SW11 and SW12 are turned on, and the semiconductor laser LD31 emits light because the sum of the bias current and the switching current is supplied to the semiconductor laser LD31. The photodiode PD31 outputs a photocurrent proportional to the light emission amount, and the photocurrent passes through a current mirror circuit composed of PMOS transistors M1 and M2 and a current mirror circuit composed of NMOS transistors M3 and M4. Are supplied to the PD terminal, and further supplied to the resistor R1 connected to the RPD terminal, and converted into a voltage by the resistor R1.

The APC control circuit 11 compares the voltage converted by the resistor R1 with a reference voltage (not shown), and adjusts the sum of the bias current and the switching current so that the voltage converted by the resistor R1 becomes equal to the reference voltage. The current value is stored in a built-in storage means.
The resistor R1 can be adjusted so that variations in the photocurrent of the photodiode PD31 and variations in the reference voltage can be corrected.
When the switching current is fixed, the bias current value is determined by the stored current value. Conversely, when the bias current is fixed, the switching current value is determined by the stored current value. Furthermore, in order to improve the accuracy, two storage means may be provided, and both the bias current and the switching current may be stored separately.

  When performing APC adjustment of the semiconductor laser LD32, the automatic light amount control signal APC2 may be set to a high level when the automatic light amount control signal APC1 is at a low level. Adjustment can be performed in exactly the same manner as the APC adjustment of the semiconductor laser LD31. Further, when the automatic light quantity control signal APC2 is set to the high level, the LDOFF terminal of the automatic light quantity control circuit 10 is set to the high level. Then, since the output signal of the inverter circuit 14 becomes low level, the LDOFFB signal becomes low level, and the switch SW12 is turned off. Since the output signal of the AND circuit 17 is also at a low level, the switch SW11 is also turned off.

  As a result, during the APC adjustment of the semiconductor laser LD32, since both the bias current and the switching current of the semiconductor laser LD31 are completely cut off, the semiconductor laser LD31 is completely turned off. For this reason, as in the prior art, semiconductor lasers other than those in the APC are lit slightly by the bias current, and a decrease in the APC adjustment accuracy due to the minute light emission can be eliminated, and highly accurate current setting can be performed. In particular, when the number of semiconductor lasers is large, errors due to slight lighting due to bias current cannot be ignored. In the first embodiment, the connection of the semiconductor lasers LD31 and LD32 in the semiconductor laser array 30 is common to the cathode, but it may be configured using a semiconductor laser array of common anode.

Second embodiment.
FIG. 2 is a diagram showing a circuit example of a semiconductor laser array light quantity control circuit according to the second embodiment of the present invention. In FIG. 2, the same or similar elements as those in FIG. 1 are denoted by the same reference numerals.
2 differs from FIG. 1 in that the current mirror circuit formed by the MOS transistors M1 to M5 is eliminated, and the PD control circuit 18 and the switch SW13 are added in the automatic light quantity control circuits 10 and 20. . The connection between the other ends of the adjustment resistors R1 and R2 is the ground voltage GND. Since the connection is determined by the circuit configuration of the PD control circuit 18, depending on the circuit configuration of the PD control circuit 18, the power supply voltage Sometimes connected to Vdd.

  The PD control circuit 18 is a circuit for amplifying the photocurrent of the photodiode PD31 to increase the sensitivity and changing the direction of the photocurrent so as to meet the specifications of the APC control circuit 11. The switch SW13 is connected between the PD terminal and the input terminal of the PD control circuit 18, and the LDOFFB signal is input to the control terminal of the switch SW13. Since the APC operation in the automatic light quantity control circuit 10 is exactly the same as that in the first embodiment, the description thereof is omitted.

  The difference from the first embodiment is that when the automatic light quantity control circuit 20 is performing the APC operation, the LDOFFB signal becomes low level and the switch SW13 is turned off. The PD terminal is in a high impedance state. For this reason, the cathode connection of the photodiode PD31 is disconnected at the PD terminal of the automatic light quantity control circuit 10, and the current mirror circuit using the MOS transistor that is necessary in the first embodiment is no longer necessary. This is the point at which OR connection becomes possible. Note that the PD control circuit 18 is not always necessary, and the current mirror circuit can be omitted even if the switch SW13 is interposed between the RPD terminal and the PD terminal of the first embodiment.

Third embodiment.
FIG. 3 is a diagram showing a circuit example of a semiconductor laser array light quantity control circuit according to the third embodiment of the present invention.
The semiconductor laser array light quantity control circuit of FIG. 3 includes two semiconductor devices 100 and 200, a semiconductor laser array 30, and adjustment resistors R1 to R4. The semiconductor devices 100 and 200 are exactly the same circuit. In FIG. 3, the same or similar parts as those in FIG. 1 or FIG.

  The semiconductor device 100 includes automatic light quantity control circuits 10 and 20, a NOR circuit 19, an APC signal generation circuit 50, a PD control circuit 18, and a switch SW13. In addition, the semiconductor device 100 includes an APC1 terminal, an APC2 terminal, an LDOFF1 terminal, an LDOFF2 terminal, an RPD1 terminal, an RPD2 terminal, a PD terminal, an LD1 terminal, an LD2 terminal, a DATA1 terminal, and a DATA2 terminal. The APC1 terminal and the APC2 terminal are first light quantity control input terminals, the LDOFF1 terminal and the LDOFF2 terminal are second light quantity control input terminals, and the APC signal generation circuit 50 is an internal automatic light quantity control signal generation circuit. The automatic light quantity control circuits 10 and 20 are exactly the same circuit.

The semiconductor laser array 30 includes four semiconductor lasers LD31 to LD34 and one photodiode PD31.
The cathodes of the semiconductor lasers LD31 to LD34 and the anode of the photodiode PD31 are connected in common and connected to the ground voltage GND. The automatic light amount control signal APC1 is input to the APC1 terminal of the semiconductor device 100 and the LDOFF1 terminal of the semiconductor device 200, respectively. The automatic light amount control signal APC2 is input to the APC2 terminal of the semiconductor device 100 and the LDOFF2 terminal of the semiconductor device 200, respectively. Has been. The automatic light amount control signal APC3 is input to the LDOFF1 terminal of the semiconductor device 100 and the APC1 terminal of the semiconductor device 200, respectively. The automatic light amount control signal APC4 is input to the LDOFF2 terminal of the semiconductor device 100 and the APC2 terminal of the semiconductor device 200. Each is entered.

  The APC1 terminal and APC2 terminal of the semiconductor device 100 are connected to the input terminal of the APC signal generation circuit 50, respectively. The LDOFF1 terminal and the LDOFF2 terminal of the semiconductor device 100 are connected corresponding to the first input terminal and the second input terminal of the NOR circuit 19. The output terminal of the NOR circuit 19 is connected to the input terminal of the APC signal generation circuit 50 and to the control terminal of the switch SW13. A resistor R1 is connected between the RPD1 terminal and the ground voltage GND, and a resistor R3 is connected between the RPD2 terminal and the ground voltage GND. The RPD1 terminal is connected to the input terminal of the APC control circuit 11, and the RPD2 terminal is connected to the input terminal of the APC control circuit 21.

  The PD terminal is connected to the cathode of the photodiode PD31 and to the input terminal of the PD control circuit 18 via the switch SW13 in the semiconductor device 100. The output terminal of the PD control circuit 18 is connected to each input terminal of the APC control circuits 11 and 21. The anode of the semiconductor laser LD31 is connected to the LD1 terminal, and the anode of the semiconductor laser LD32 is connected to the LD2 terminal. The connection of the semiconductor device 200 is the same as that of the semiconductor device 100 except for the automatic light quantity control APC1 to APC4.

The automatic light quantity control circuit 10 includes an APC control circuit 11, a switching current generation circuit 12, a bias current generation circuit 13, AND circuits 15 and 17, an OR circuit 16, and switches SW11 and SW12.
From the APC signal generation circuit 50, the IAPC1 signal and the IAPC2 signal which are internal APC signals actually used by the automatic light quantity control circuits 10 and 20, and a signal for prohibiting the operation of other automatic light quantity control circuits during the APC operation. The LDOFF10 signal and the LDOFF20 signal are output.

  The IAPC1 signal is input to the second input terminal of the AND circuit 15 and the first input terminal of the OR circuit 16, and the LDOFF10 signal is input to the first input terminal of the AND circuit 15, the first input terminal of the AND circuit 17, and the switch. Each is input to the control terminal of SW12. Similarly, the IAPC2 signal is input to the second input terminal of the AND circuit 25 and the first input terminal of the OR circuit 26, and the LDOFF20 signal is input to the first input terminal of the AND circuit 25 and the first input terminal of the AND circuit 27. , And the control terminal of the switch SW22.

An output terminal of the AND circuit 15 is connected to an input terminal of the APC control circuit 11, and an output terminal of the APC control circuit 11 is input to each input terminal of the switching current generation circuit 12 and the bias current generation circuit 13. The output terminal of the switching current generation circuit 12 is connected to one end of the switch SW11, and the other end of the switch SW11 is connected to the LD1 terminal. The output terminal of the bias current generation circuit 13 is connected to one end of the switch SW12, and the other end of the switch SW12 is connected to the LD1 terminal.
The second input terminal of the OR circuit 16 is connected to the DATA 1 terminal, and the output terminal of the OR circuit 16 is connected to the second input terminal of the AND circuit 17. The output terminal of the AND circuit 17 is connected to the control terminal of the switch SW11. Since the connection of the automatic light quantity control circuit 20 is the same as that of the automatic light quantity control circuit 10, the description thereof is omitted.

FIG. 4 is a diagram showing a circuit example of the APC signal generation circuit 50 of FIG.
4, the APC signal generation circuit 50 includes four AND circuits 53 to 56, NOR circuits 57 and 58, inverter circuits 59 and 60, and two delay circuits 51 and 52.
In the AND circuit 53, the first input terminal is connected to the APC1 terminal, the LDOFFALL signal that is the output signal of the NOR circuit 19 is input to the second input terminal, the output terminal is the input terminal of the delay circuit 51, and the AND circuit 54 The second input terminal and the first input terminal of the NOR circuit 57 are respectively connected. The output terminal of the delay circuit 51 is connected to the first input terminal of the AND circuit 54, and the IAPC1 signal that is an internal APC signal is output from the output terminal of the AND circuit 54. A signal obtained by inverting the LDOFFALL signal by the inverter circuit 60 is input to the second input terminal of the NOR circuit 57, and the LDOFF 20 signal is output from the output terminal of the NOR circuit 57.

  In the AND circuit 55, a signal obtained by inverting the APC1 signal by the inverter circuit 59 is input to the first input terminal, the LDOFFALL signal is input to the second input terminal, and the third input terminal is connected to the APC2 terminal. The output terminal of the AND circuit 55 is connected to the input terminal of the delay circuit 52, the second input terminal of the AND circuit 56, and the second input terminal of the NOR circuit 58. The output terminal of the delay circuit 52 is connected to the second input terminal of the AND circuit 56. Connected to one input end. An IAPC2 signal that is an internal APC signal is output from the output terminal of the AND circuit 56. A signal obtained by inverting the LDOFFALL signal by the inverter circuit 60 is input to the second input terminal of the NOR circuit 57, and the LDOFF20 signal is output from the output terminal. Similarly, a signal obtained by inverting the LDOFFALL signal by the inverter circuit 60 is input to the first input terminal of the NOR circuit 58, and the LDOFF10 signal is output from the output terminal.

FIG. 5 is a timing chart for explaining the operation of the semiconductor laser array light quantity control circuit of FIG. 4. The operation of the semiconductor laser array light quantity control circuit of FIG. 4 will be described with reference to FIG.
In FIG. 5, first, the state of each signal when the automatic light quantity control signals APC1 to APC4 are all at the low level at time t0 will be described. Since both the APC3 signal and the APC4 signal are at the low level, the LDOFFALL signal that is the output signal of the NOR circuit 19 is at the high level. Since the APC1 signal is at a low level, the output signal of the AND circuit 53 is at a low level, and the output signal of the AND circuit 54 is also at a low level, so the internal automatic control signal IAPC1 is at a low level. Since the low level obtained by inverting the high-level LDOFFALL signal by the inverter circuit 60 is input to the second input terminal of the NOR circuit 57, the LDOFF20 signal that is the output signal of the NOR circuit 57 is high level.

Since the APC2 signal is at a low level, the output signal of the AND circuit 55 is at a low level, the output signal of the AND circuit 56 is also at a low level, and the internal automatic control signal IAPC2 is at a low level. Since the low level obtained by inverting the high-level LDOFFALL signal by the inverter circuit 60 is input to the first input terminal of the NOR circuit 58, the LDOFF10 signal that is the output signal of the NOR circuit 58 is high level.
Under such signal conditions, the APC control circuits 11 and 21 in the semiconductor device 100 are not operated, and the switches SW12 and SW22 are on. Further, the switches SW11 and SW21 are on / off controlled by data signals at the DATA1 terminal and the DATA2 terminal, and the switch SW13 is on.

  When the automatic light quantity control signal APC1 becomes high level at time t1, both the first input terminal and the second input terminal of the AND circuit 53 become high level, so that the output signal of the AND circuit 53 becomes high level. Then, since the first input terminal of the NOR circuit 57 becomes high level, the LDOFF20 signal which is the output signal of the NOR circuit 57 becomes low level. When the LDOFF20 signal becomes low level, the switch SW22 is turned off. Further, since the output signal of the AND circuit 27 is also at a low level, the switch SW21 is also turned off, and the bias current and switching current to the LD2 terminal are completely cut off. For this reason, since the semiconductor laser LD32 is completely turned off, the automatic light quantity control circuit 10 that performs APC of the semiconductor laser LD31 is not adversely affected.

When the output signal of the AND circuit 53 becomes high level at time t1, the signal is delayed by a predetermined time td by the delay circuit 51, and the first input terminal of the AND circuit 54 becomes high level at time t2. For this reason, the IAPC1 signal, which is an internal APC signal, becomes high level at a time t2 when a predetermined time td has elapsed since the APC1 signal became high level, and the operation of the APC control circuit 11 of the automatic light quantity control circuit 10 starts.
When the IAPC1 signal becomes high level, the output signal of the OR circuit 16 becomes high level regardless of the signal of the DATA1 terminal. Therefore, the output signal of the AND circuit 17 becomes high level, the switch SW11 is turned on, and the bias current and A switching current is supplied to the semiconductor laser LD31 via the LD1 terminal. Since the LDOFFALL signal is at a high level, the switch SW13 is on and the photocurrent of the photodiode PD31 is input to the PD control circuit 18.

When the APC1 signal returns to the low level at the time t3, the output signal of the AND circuit 53 becomes the low level. Therefore, the output signal of the AND circuit 54 also becomes the low level, the IAPC1 signal also returns to the low level, and the APC of the semiconductor laser LD31 changes. finish. Also, the LDOFF20 signal returns to the high level and is in the same state as at time t0.
Next, when only the APC2 signal becomes high level at time t4, the output signal of the AND circuit 55 becomes high level, the LDOFF10 signal that is the output signal of the NOR circuit 58 becomes low level, and further, the delay circuit 52 performs predetermined processing. The time IAd is delayed, and at time t5, the IAPC2 signal, which is an internal APC signal, becomes high level. When the IAPC2 signal becomes high level, APC of the automatic light quantity control circuit 20 starts. Since the operation of each part is the same as the operation described in the automatic light quantity control circuit 10, the description thereof is omitted.

When the APC2 signal returns to the low level at time t6, the output signal of the AND circuit 55 becomes the low level, so the output signal of the AND circuit 56 also becomes the low level, the IAPC2 signal becomes the low level, and the LDOFF10 signal becomes the high level. Returning to each other, the APC of the semiconductor laser LD32 is completed.
When the APC1 signal and the APC2 signal simultaneously become high level at time t7, the output signal of the AND circuit 53 becomes high level and the LDOFF20 signal becomes low level, but the first input terminal of the AND circuit 55 is the output of the inverter circuit 59. Since the signal becomes low level, the output signal of the AND circuit 55 remains at low level. For this reason, the IAPC1 signal has priority over the internal APC signal, and only the IAPC1 signal becomes high level at time t8 when the predetermined delay time td has elapsed. Since the operation when the IAPC1 signal is at the high level is the same as described above, the description thereof is omitted.

When the APC1 signal returns to low level at time t9, the IAPC1 signal returns to low level and the LDOFF20 signal returns to high level. However, since the APC2 signal is still at the high level at this time, the output signal of the AND circuit 55 becomes the high level, and the LDOFF10 signal becomes the low level. Further, at time t10 after a predetermined delay time td, the IAPC2 signal becomes high level, and APC of the automatic light quantity control circuit 20 is performed.
When the APC2 signal returns to low level at time t11, the IAPC2 signal also returns to low level, and the LDOFF10 signal returns to high level.

Next, a case where the semiconductor device 200 performs APC will be described.
When the APC3 signal or APC4 signal becomes high level, the automatic light amount control circuit in the semiconductor device 200 operates.
When the APC3 signal or APC4 signal becomes high level at time t12, the LDOFFALL signal becomes low level. Then, since the first input terminal of the AND circuit 53 and the second input terminal of the AND circuit 55 are at the low level, even if the APC1 signal becomes high level at time t13 and the APC2 signal becomes high level at time t14, the internal APC signal Since the IPAC1 signal and the IAPC2 signal are not at a high level, the automatic light quantity control circuits 10 and 20 of the semiconductor device 100 do not perform APC.

  Further, when the LDOFFALL signal becomes low level, the second input terminal of the NOR circuit 57 and the first input terminal of the NOR circuit 58 become high level, respectively, so that both the LDOFF10 signal and the LDOFF20 signal become low level. As a result, the switches SW11, SW12, SW21, and SW22 in the semiconductor device 100 are all turned off, and both the bias current and the switching current to the LD1 terminal and the LD2 terminal are cut off. Therefore, APC is performed in the semiconductor device 200. In this case, all the semiconductor lasers connected to the semiconductor device 100 are completely turned off, and the APC of the semiconductor device 200 is not adversely affected.

  Further, since the LDOFFALL signal is at a low level, the switch SW13 is also turned off, and the connection between the anode of the photodiode PD31 and the input terminal of the PD control circuit 18 in the semiconductor device 100 is also cut off. Therefore, the current mirror circuit by the MOS transistors M1 to M5 shown in the first embodiment is not necessary, which greatly contributes to downsizing and low cost. can do.

At time t15, the APC1 signal becomes high level. At this time, since the LDOFFALL signal is at low level, the IAPC1 signal remains at low level.
When the APC of the semiconductor device 200 ends at time t16 and the LDOFFALL signal becomes high level, the IAPC1 signal becomes high level at time t17 after the delay time td, and the automatic light quantity control circuit 10 starts APC.
As described above, even when the automatic light quantity control signals APC1 to APC4 are simultaneously output to the semiconductor devices 100 and 200, APC can be started when all of the APC signals of the other semiconductor devices become low level. APC of all semiconductor lasers can be executed efficiently.

Since the semiconductor devices 100 and 200 have exactly the same circuit configuration as described above, when the semiconductor device 100 performs APC, the currents to the semiconductor lasers LD33 and LD34 connected to the semiconductor device 200 Needless to say, the supply is completely cut off, and the connection between the photodiode PD31 and the PD control circuit in the semiconductor device 200 is also cut off.
Furthermore, when the APC signal of the other semiconductor device becomes high level while one of the semiconductor devices is performing APC, the APC of the semiconductor device performing APC is stopped, and the APC of both semiconductor devices is Since it is prohibited, it is possible to avoid problems caused by simultaneously executing APC.

Furthermore, since the delay time td is provided before the APC is performed, even when the APC is continuously performed, the next APC does not start until the predetermined time td has elapsed after the previous APC is completed. APC mutual interference can be completely eliminated.
In the third embodiment, the case where there are two semiconductor devices has been described as an example. However, the present invention is not limited to the case where there are two semiconductor devices, and there are three or more semiconductor devices. The present invention can also be applied when using a semiconductor device.

It is the figure which showed the circuit example of the semiconductor laser array light quantity control circuit in the 1st Embodiment of this invention. It is the figure which showed the circuit example of the semiconductor laser array light quantity control circuit in the 2nd Embodiment of this invention. It is the figure which showed the circuit example of the semiconductor laser array light quantity control circuit in the 3rd Embodiment of this invention. FIG. 4 is a diagram illustrating a circuit example of an APC signal generation circuit 50 in FIG. 3. 4 is a timing chart showing an operation example of the circuit of FIG. 3.

Explanation of symbols

10, 20 Automatic light quantity control circuit 30 Semiconductor laser array 11, 21 APC control circuit 12, 22 Switching current generation circuit 13, 23 Bias current generation circuit 18 PD control circuit 50 APC signal generation circuit (internal automatic light quantity control signal generation circuit)
100, 200 Semiconductor device LD31-LD34 Semiconductor laser PD31 Photodiode APC1-APC4 Automatic light quantity control signal IAPC1, IAPC2 Internal automatic light quantity control signal

Claims (14)

In a semiconductor laser array light quantity control circuit for controlling the light quantity of a semiconductor laser array having a plurality of semiconductor lasers,
A light receiving element for receiving the amount of light output from each of the semiconductor lasers;
In response to the input automatic light amount control signal, each automatic light amount control circuit that performs control to set the light emission amount output from the corresponding semiconductor laser to a predetermined light emission amount according to the output of the light receiving element;
With
Each of the automatic light quantity control circuits inputs the automatic light quantity control signal input to itself to the other automatic light quantity control circuit, thereby prohibiting the operation of the other automatic light quantity control circuit and corresponding the semiconductor laser. While the automatic light quantity control is performed in accordance with the automatic light quantity control signal input by one of the automatic light quantity control circuits, the other automatic light quantity control circuits operate so as to cut off the current supply to The semiconductor laser array light quantity control circuit is characterized in that the current supply to the corresponding semiconductor laser is cut off to stop the current supply. Each automatic light quantity control circuit is
A first light amount control input terminal to which the automatic light amount control signal for performing the automatic light amount control is input to the corresponding semiconductor laser;
One or more second light quantity control input terminals for inputting the automatic light quantity control signal to the other automatic light quantity control circuits;
With
2. When the automatic light amount control signal is input to any one of the second light amount control input terminals, the operation is stopped and the current supply to the corresponding semiconductor laser is cut off. The semiconductor laser array light quantity control circuit of description.   Each of the automatic light quantity control circuits inputs the automatic light quantity control signal input to the first light quantity control input terminal to the second light quantity control input terminal of the other automatic light quantity control circuit. 3. The semiconductor laser array light quantity control circuit according to claim 2, wherein the operation of the automatic light quantity control circuit is prohibited to interrupt the current supply to the corresponding semiconductor laser.   Each of the automatic light amount control circuits includes a photocurrent input terminal to which a photocurrent output from the light receiving element is input, and while the other automatic light amount control circuits are operating, the photocurrent input terminal 4. The semiconductor laser array light quantity control circuit according to claim 1, wherein the photocurrent input terminal is interrupted to place the photocurrent input terminal in a high impedance state. A plurality of semiconductor devices having a plurality of automatic light quantity control circuits,
Each of the semiconductor devices is
Each first light amount control input terminal to which each of the automatic light amount control signals for operating each of the built-in automatic light amount control circuits is input correspondingly;
Each second light quantity control input terminal to which the respective automatic light quantity control signals for operating the respective automatic light quantity control circuits in the other semiconductor devices are input correspondingly;
With
While the automatic light quantity control signal is inputted to one of the semiconductor devices and the automatic light quantity control is performed, the operation of the other automatic light quantity control circuits built in and the respective automatic light quantity control circuits built in the other semiconductor devices are performed. 5. The semiconductor laser array light quantity according to claim 1, wherein the current supply to all the semiconductor lasers connected to the automatic light quantity control circuit that inhibits the operation is blocked. Control circuit.   Each of the semiconductor devices prohibits the operation of all of the built-in automatic light amount control circuits when the automatic light amount control signal is input to any of the second light amount control input terminals, and 6. The semiconductor laser array light quantity control circuit according to claim 5, wherein all current supply to each semiconductor laser connected in correspondence with the control circuit is cut off.   Each of the automatic light quantity control circuits inputs the automatic light quantity control signal input to the first light quantity control input terminal to the second light quantity control input terminal of the other automatic light quantity control circuit. 7. The semiconductor laser array light quantity control circuit according to claim 6, wherein the operation of the automatic light quantity control circuit is prohibited to cut off all current supply to the corresponding semiconductor laser.   Each of the semiconductor devices includes a photocurrent input terminal to which a photocurrent output from the light receiving element is input, and while the automatic light quantity control circuit in another semiconductor device is operating, the light 8. The semiconductor laser array light quantity control circuit according to claim 5, wherein the photocurrent input terminal is cut off to put the photocurrent input terminal into a high impedance state.   Each of the semiconductor devices includes an internal automatic light quantity control signal generation circuit that inputs the automatic light quantity control signal input to the plurality of first light quantity control input terminals and generates an internal automatic light quantity control signal. The light amount control signal generation circuit generates one internal automatic light amount control signal according to a predetermined priority when a plurality of the automatic light amount control signals are simultaneously input. 9. The semiconductor laser array light quantity control circuit according to 8.   10. The semiconductor laser array light quantity control according to claim 9, wherein the internal automatic light quantity control signal generation circuit outputs the internal automatic light quantity control signal after a predetermined time elapses with respect to the automatic light quantity control signal. circuit.   The internal automatic light amount control signal generation circuit, when a plurality of the automatic light amount control signals are input simultaneously, after the predetermined time has elapsed after the input of the automatic light amount control signal having a high priority is completed. 11. The semiconductor laser array light quantity control circuit according to claim 10, wherein the next internal automatic light quantity control signal is output.   The internal automatic light quantity control signal generation circuit, when the automatic light quantity control signal of the other semiconductor device is all turned off from the state where the automatic light quantity control signal is simultaneously input to the semiconductor device and the other semiconductor device. 12. The semiconductor laser array light quantity control circuit according to claim 9, wherein the internal automatic light quantity control signal is output after a predetermined time has elapsed.   When the automatic light amount control signal is input simultaneously with another semiconductor device, the semiconductor device inhibits all the automatic light amount control circuits built therein and interrupts all current supply to the corresponding semiconductor laser. 13. The semiconductor laser array light quantity control circuit according to claim 5, 6, 7, 8, 9, 10, 11 or 12.   An image forming apparatus using the semiconductor laser array light quantity control circuit according to any one of claims 1 to 13.

Images