JP2015204358A - semiconductor laser driving apparatus and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser driving apparatus capable of detecting characteristics of a semiconductor laser in a predetermined period and initializing the semiconductor laser.SOLUTION: A semiconductor laser driving apparatus for controlling drive of a semiconductor laser by controlling a current to be supplied to a semiconductor laser so as to obtain a desired light emission quantity by initialization processing includes: an initialization circuit for dividing the initialization processing in a plurality of non-image regions to perform the initialization processing; and a storage circuit for storing current setting values of a bias current and a light-emitting current during interruption of the initialization processing. The initialization circuit starts the initialization processing, when an initialization signal becomes valid, and interrupts the initialization processing when the initialization signal becomes invalid on the way of the initialization processing, and stores the current setting values of the bias current and the light-emitting current during the interruption of the initialization processing in the storage circuit, and then when the initialization becomes valid, reads the current setting values during the interruption from the storage circuit, sets the read values and restarts the initialization processing from a state of the interruption.

Description

  The present invention relates to a semiconductor laser driving apparatus and method, and more particularly, to a semiconductor laser initialization process.

  A semiconductor laser is small and inexpensive, and can easily obtain laser light simply by flowing current. Therefore, it is widely used in the fields of printers, optical disks, optical communication, and the like (see, for example, Patent Document 1). However, since the amount of light emitted from a semiconductor laser is temperature-dependent, special light amount control is required to obtain a constant light amount. In general, this light quantity control is called initialization or APC (Automatic Power Control) (see, for example, Patent Document 1).

  The APC correction method is a method of redetecting the threshold current Ith of the semiconductor laser, and is not a means for correcting the slope η of the drive current Iη with respect to the light emission amount. Also, if APC is performed in the non-image area when the slope η of the drive current Iη is reduced due to the temperature characteristics of the semiconductor laser, Iη> Isw. Here, Isw is a light emission current, and since an insufficient amount of the light emission current Isw is corrected by the bias current Ithon, Ithon> Ith, and there is a possibility that light emission is always performed (see FIG. 10D described later). In the opposite case, Ith >> Ithon, and there is a problem that the response at the time of lighting is lowered. Further, when the bias current Ithon is made sufficiently low to prevent light emission at all times, there is a problem that the response at the time of lighting is lowered.

  For example, in Patent Document 1, in order to solve the problem of constant over-emission due to a decrease in differential efficiency, initialization is performed at normal temperature and at high temperature, respectively, so that the threshold current Ith changes from normal temperature to high temperature are greater than or equal to each other. Auxiliary current Isub is set. Since the sample and hold current Ish is set lower than the threshold current Ith by the auxiliary current Isub, the problem that the responsiveness is lowered cannot be solved.

  An object of the present invention is to solve the above problems and provide a semiconductor laser driving apparatus capable of detecting and initializing characteristics of a semiconductor laser in a predetermined period.

The semiconductor laser driving device according to the present invention controls the current supplied to the semiconductor laser so that a desired light emission amount can be obtained by the initialization process, and controls the driving of the semiconductor laser.
An initialization circuit that divides the initialization process in a plurality of non-image areas;
A storage circuit for storing a current setting value of a bias current and a light emission current when the initialization process is interrupted,
The initialization circuit includes:
When the initialization signal becomes valid, the initialization process starts.
When the initialization signal becomes invalid during the initialization process, the initialization process is interrupted, and the current setting values of the bias current and the light emission current at the interruption of the initialization process are stored in the storage circuit. Then, when the initialization signal becomes valid, the current setting value at the time of interruption is read and set from the storage circuit, and the initialization process is restarted from the state at the time of interruption. .

  Therefore, according to the present invention, by performing reinitialization when the characteristics of the semiconductor laser change after initialization, the light emission current and the bias current are appropriately reset according to the electrical characteristics of the semiconductor laser, and stored. Since the reinitialization state is stored in the circuit, the initialization (reinitialization) can be performed little by little in the non-image area.

It is a block diagram which shows the structure of the semiconductor laser drive device which concerns on Embodiment 1 of this invention. 3 is a flowchart showing a reinitialization process executed by the initialization circuit 3 of the semiconductor laser driving device of FIG. 1. 3 is a timing chart showing a reinitialization process of the semiconductor laser driving device of FIG. 1. It is a block diagram which shows the structure of the semiconductor laser drive device which concerns on Embodiment 2 of this invention. 5 is a flowchart showing a reinitialization process executed by the initialization circuit 3 of the semiconductor laser driving device of FIG. 4. 2 is a timing chart showing a reinitialization process of the semiconductor laser drive device of FIG. 1, wherein (a) shows that the control circuit 14 initializes an initialization completion signal Sre_inend when the reinitialization result reflection signal Sinend_en changes from a low level to a high level. FIG. 8B is a diagram illustrating an example of controlling the reflection timing of the initialization result from the value of (b), and (b) does not reflect the reinitialization result when the reinitialization result discard signal Sinend_dis changes from the low level to the high level. It is a figure which shows an example which controls starting to re-initialize forcibly. It is a block diagram which shows the structure of the semiconductor laser drive device which concerns on Embodiment 3 of this invention. It is a flowchart which shows the main routine of the re-initialization process performed by the initialization circuit 3 of the semiconductor laser drive device of FIG. It is a flowchart which shows the interruption process of the reinitialization process performed by the initialization circuit 3 of the semiconductor laser drive device of FIG. It is a timing chart which shows the re-initialization process of the semiconductor laser drive device of FIG. It is a graph which shows the relationship between each electric current and light emission amount in a comparative example and embodiment.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In addition, in each following embodiment, the same code | symbol is attached | subjected about the same component.

Embodiment 1. FIG.
FIG. 1 is a block diagram showing a configuration of a semiconductor laser driving apparatus for an image forming apparatus such as a printer according to Embodiment 1 of the present invention. According to the present embodiment, the drive of the semiconductor laser is controlled by controlling the current supplied to the semiconductor laser so that a desired light emission amount can be obtained by the initialization process. The semiconductor laser driving device is particularly characterized as follows.
(1) In the re-initialization in the non-image area, even in a semiconductor laser diode (hereinafter referred to as a laser diode) LD in which the slope η of the drive current Iη with respect to the light emission amount changes following the temperature change, in the non-image area. The drive current Iη is appropriately set by performing initialization (referred to as reinitialization). Here, when the image region in the main scanning direction of the image forming apparatus is specified by the start synchronization signal and the end synchronization signal, the “non-image region”
(A) A section from an end synchronization signal of a certain main scanning line to a start synchronization signal of the next main scanning line, and (B) a section between sheets between sheets on which an image is formed. This is a section from the end synchronization signal of the last main scanning line of the paper to the start synchronization signal of the first main scanning line of the next paper. Hereinafter, it is referred to as “non-image area”.
(2) Reinitialization is performed in readjustment when the electrical characteristics change due to the temperature characteristics of the laser diode LD after initialization. Thereby, the light emission current and the bias current (Isw, Ithon, Itoff, etc.) of the semiconductor laser driving device are reset appropriately according to the temperature characteristics of the laser diode LD. Here, in the semiconductor laser driving device, each circuit excluding the laser diode LD and the photodiode PD in FIG. 1 is configured by, for example, an integrated circuit (IC).
(3) Reinitialization is intermittently performed by storing the reinitialization state (current values corresponding to the digital control signals SD2, SD3, SD4) in the register of the storage circuit 4.
(4) Reinitialization is performed in a plurality of times even in a short period where initialization is impossible, such as a non-image area. After the reinitialization is completed, the reinitialization data is automatically reflected or after the completion signal is received, the user reflects or discards the reinitialization data at an arbitrary timing.

  In FIG. 1, a semiconductor laser driving device includes a comparison circuit 1, an initialization circuit 3, a storage circuit 4 that stores a state during re-initialization, a reference voltage source 6 that generates a reference voltage Vr, and a voltage dividing circuit. 7. The semiconductor laser drive device further includes a drive current switch circuit 8, a bias current generation circuit 9, a bias current generation circuit 10, a light emission current generation circuit 11, an auxiliary current generation circuit 12, a selection circuit 13, and an OR gate 16. It is configured with. As an external device of the semiconductor laser driving apparatus, a controller 20 of the image forming apparatus, a laser diode LD that emits light with a predetermined driving current Iop, and a photodiode that detects the light emission amount of the laser diode LD and outputs an output voltage Vpd. A PD and a variable resistor 5 are provided.

  In FIG. 1, the voltage dividing circuit 7 divides the reference voltage Vr by a predetermined voltage dividing ratio based on the control signal S2 from the initialization circuit 3, for example, by resistance voltage division, in accordance with the control signal S2 input from the initialization circuit 3. The divided reference voltage Vc is output to the non-inverting input terminal of the comparison circuit 1. The comparison circuit 1 compares the output voltage Vpd of the photodiode PD input to the inverting input terminal with the divided reference voltage Vc from the voltage dividing circuit 7, and compares the comparison result voltage Vd that is a difference voltage of the comparison result. Is output to the initialization circuit 3. The initialization circuit 3 generates and outputs various signals based on various input signals by executing an initialization process shown in FIG. 2 described later. The bias current generation circuit 9 detects the oscillation threshold current of the laser diode LD in response to the digital signal SD2 from the initialization circuit 3. Based on the detected oscillation threshold current, the bias current generation circuit 9 generates a bias current Iton for turning on the semiconductor laser with an oscillation threshold current that changes according to an input signal for image formation. And output to the selection circuit 13. The bias current generation circuit 10 generates and selects a bias current Ibi (current value less than the oscillation threshold current) obtained by multiplying the oscillation threshold current by a predetermined coefficient in accordance with the input digital signal SD2. Always output to the circuit 13. The light emission current generation circuit 11 drives the light emission current Isw for emitting the laser diode LD according to the digital signal SD3 from the initialization circuit 3 so that the detected light emission amount of the laser diode LD becomes a desired value. Output to the switch circuit 8. The auxiliary current generation circuit 12 generates a predetermined auxiliary current Isub based on the digital signal SD4 from the initialization circuit 3 and outputs it to the drive current switch circuit 8.

  Here, the initialization circuit 3 executes an initialization process for detecting the light emission characteristics of the laser diode LD, and generates a digital signal SD2 indicating the current value of the bias current Ithon obtained from the detected light emission characteristics. Output to the circuit 9. In response to this, the bias current generation circuit 9 generates a current so that the bias current Ithon flows through the laser diode LD. In addition, the initialization circuit 3 uses the digital signal SD3 so that the light emission current Isw becomes a desired value so that the light emission amount of the laser diode LD due to the sum of the bias current Ithon, the light emission current Isw, and the auxiliary current Isub becomes a desired value. And output to the light emission current generation circuit 11. In response to this, the light emission current generation circuit 11 generates a current so that the light emission current Isw flows through the laser diode LD so that the light emission amount of the laser diode LD by the sum current becomes a desired value.

The OR gate 16 generates a control signal Si4 that is a logical sum of the control signal Si3 from the initialization circuit 3 and the control signal Si1 from the controller 20 of the image forming apparatus, and outputs the control signal Si4 to the drive current switch circuit 8. The drive current switch circuit 8 includes the following switches SW1 to SW3 that are turned on / off based on the control signal Si4, and generates the control signal S3 to control the selection circuit 13.
(1) A switch SW1 for controlling whether or not to apply a bias current from the selection circuit 13 to the laser diode LD;
(2) A switch SW2 for controlling whether or not the light emission current Isw from the light emission current generation circuit 11 is supplied to the laser diode LD; and (3) whether or not the auxiliary current Isub from the auxiliary current generation circuit 12 is supplied to the laser diode LD. A switch SW3 for controlling the above.

  The selection circuit 13 selects the bias current Ithon or Ibi as the current to be output to the drive current switch circuit 8 according to the control signal S3 from the drive current switch circuit 8, and outputs the selected bias current Iton or Ibi to the switch SW1 of the drive current switch circuit 8. . Here, when the control signal S3 is at a high level, the bias current Ithon from the bias current generation circuit 9 is selected and output. When the control signal S3 is at a low level, the bias current Ibi from the bias current generation circuit 10 is selected and output.

  The initialization circuit 3 is supplied with an initialization signal Si2 (indicating initialization or reinitialization and indicating a non-image area) and a predetermined clock signal CLK from the controller 20 of the image forming apparatus, which is an external circuit, for example. The comparison result voltage Vd of the comparison result from the comparison circuit 1 is input. The initialization circuit 3 detects the electrical characteristics of the laser diode LD and controls the operation of the voltage dividing circuit 7 when performing the initialization operation or the reinitialization operation for setting the digital control signals SD2 and SD3. The voltage dividing ratio of the voltage dividing circuit 7 is controlled using the control signal S2. Here, the initialization circuit 3 sets the current of the bias current generation circuits 9 and 10 by the digital control signal SD2, sets the current of the light emission current generation circuit 11 by the digital control signal SD3, and also sets the current by the digital control signal SD4. The current of the bias current generation circuit 12 is set. Further, when the re-initialization is completed, the initialization circuit 3 outputs an initialization completion signal Sre_inend to the controller 20 of the image forming apparatus that is an external circuit.

  The drive current switch circuit 8 generates and selects the control signal S3 according to the control signal Si4 of the logical sum of the light emission input signal Si1 from the controller 20 of the image forming apparatus and the control signal Si3 from the initialization circuit 3. Output to the circuit 13. When the control signal Si4 is at a high level, the bias current Ithon is output from the selection circuit 13 by the Isw output from the light emission current generation circuit 11, the auxiliary current Isub output from the auxiliary current generation circuit 12, and the control signal S3. The sum of the currents Isw, Isub, and Ithon is caused to flow through the laser diode LD by the drive current switch circuit 8 as the drive current Iop. On the other hand, when the control signal Si4 is at a low level, the bias current Ibi is output from the selection circuit 13 by the control signal S3, and the bias current Ibi is passed through the laser diode LD as the drive current Iop by the drive current switch circuit 8.

  The photodiode PD monitors the light emission amount of the laser diode LD and supplies a current proportional to the light emission amount of the laser diode LD to the variable resistor 5. The variable resistor 5 passes the current supplied from the photodiode PD through the variable resistor 5 to convert it into a voltage Vpd, and the voltage Vpd is applied to the inverting input terminal of the comparison circuit 1. The reference voltage Vc from the voltage dividing circuit 7 is output to the non-inverting input terminal of the comparison circuit 1. The comparison circuit 1 outputs a comparison result voltage Vd indicating the potential difference corresponding to the potential difference between the voltage at the non-inverting input terminal of the comparison circuit 1 and the voltage at the inverting input terminal. Here, the reference voltage Vc of the voltage dividing circuit 7 controls the comparison result voltage Vd of the comparison circuit 1 by the comparison circuit 1 so that the input voltage Vpd is equal to the reference voltage Vc.

  After the power is turned on, the initialization circuit 3 starts an initialization process in response to an initialization signal Si2 from the controller 20 of the image forming apparatus which is an external circuit. A current flows from the laser diode LD to the drive current switch circuit 8, and the laser diode LD starts to emit light. The comparison result voltage Vd of the comparison circuit 1 is input to the initialization circuit 3, and the initialization circuit 3 increases or decreases the currents Ithon, Ibi, Isw of the current generation circuits 9, 10, 11 depending on the value of the comparison result voltage Vd. Judge whether to make it. A light emission threshold current Ith is detected by the initialization circuit 3 based on the comparison result voltage Vd, and a value obtained by dividing the auxiliary current Isub from the light emission threshold current Ith is a current Ithon, and a bias current is generated by the digital control signal SD2. Set to circuit 9. Further, the bias current generating circuit 10 uses the value obtained by dividing the auxiliary current Isub from the light emission threshold current Ith of the laser diode LD by the arbitrarily set coefficient α as the bias current Ibi, and the digital control signal SD2 Thus, the bias current generating circuit 10 is set. Further, the light emission current Isw of the light emission current generation circuit 11 is set by the initialization circuit 3 so that the output voltage Vpd and the reference voltage Vc are equal. Further, the auxiliary current Isub of the auxiliary current generating circuit 12 is set to a predetermined fixed value by the digital control signal SD4 of the initialization circuit 3.

  FIG. 2 is a flowchart showing a reinitialization process executed by the initialization circuit 3 of the semiconductor laser driving device of FIG. In the semiconductor laser driving device of FIG. 1, it is assumed that the initialization of the laser diode LD is completed for easy explanation.

(Step S1) The initialization circuit 3 starts reinitialization in response to the initialization signal Si2. At this time, output of each current Ithon, Ibi, Isw, Isub is stopped by the digital control signals SD2, SD3, SD4. During the reinitialization, the control signal Si1 is at a low level and is in an invalid state.
(Step S2) An initialization process is executed.
(Step S3) It is determined whether or not the initialization process is completed. When the initialization process is completed, the process proceeds to step S7. If the initialization process is in progress, the process proceeds to step S4.
(Step S4) It is determined whether or not the control signal Si2 is ON. If the control signal Si2 is high and on, the process proceeds to step S2 and the initialization process is continued. On the other hand, when the control signal Si2 is at the low level and is off, the initialization process is interrupted (step S5) and the process proceeds to step S6.
(Step S6) It is determined whether or not the control signal Si2 is ON. When the control signal Si2 is at the high level and is on, the process proceeds to step S2 and the initialization process is restarted. On the other hand, when the control signal Si2 is at the low level and is off, the process proceeds to step S5 and the initialization process is interrupted.
(Step S7) An initialization completion signal Sre_inend is output at a high level for a predetermined period for one pulse to notify the controller 20 of the image forming apparatus, which is an external circuit, that the reinitialization process has been completed.
(Step S8) The currents Isw and Iton re-detected in the reinitialization process are reflected in the bias current generation circuit 9 and the light emission current generation circuit 11 using the digital control signals SD3 and SD2, respectively, and the reinitialization process ends. To do.

  Here, the reinitialization process of FIG. 2 is repeatedly executed while the control signal Si2 is at the high level and is valid. If the control signal Si2 becomes low level and becomes invalid during the reinitialization process, the current setting value of the storage circuit 4 is retained, and the next time the control signal Si2 becomes valid, Re-initialization can be resumed from the middle of the initialization process. Here, the current setting value refers to a current value corresponding to the digital control signals SD2, SD3, SD4.

  FIG. 3 is a timing chart showing a reinitialization process of the semiconductor laser driving device of FIG. In FIG. 3, Si2 represents a reinitialization signal, Ssw_d represents a current setting value (register) of the light emission current generation circuit 11, Sth_d represents a current setting value (register) of the bias current generation circuit 9, and Sre_inend represents an initialization completion signal. Note that the initial value of the current set value Ssw_d is c1, and the initial value of the current set value Sth_d is a1. As shown in FIG. 3, in the semiconductor laser driving apparatus for controlling the current supplied to the semiconductor laser so that a desired light emission amount can be obtained by the initialization process, the initialization circuit 3 includes: The initialization process is divided and performed in a plurality of non-image areas.

(T1) When the control signal Si2 becomes high level, a re-initialization state is established and initialization is executed. In the reinitialization state, the current setting values Ssw_d and Sth_d are sequentially updated according to the initialization.
(T2) When the control signal Si2 becomes low level, the reinitialization process is interrupted, the state at the time of interruption is written to the memory circuit 4, and the values of the current setting values Ssw_d and Sth_d return to c1 and a1, respectively.
(T3) When the control signal Si2 becomes high level again, reinitialization is resumed from the state where it was interrupted last time. The reinitialization process from t1 to t3 is repeated until the initialization is completed.
(T4) When initialization is completed, the initialization circuit 3 outputs a pulse of the initialization completion signal Sre_inend once.
(T5) Thereafter, when the control signal Si2 becomes a low level, the light emission current Isw and the bias current Ithon (e1, b1 in FIG. 3) are reflected corresponding to the detected current setting values Ssw_d and Sth_d. Next, the processing returns to time t1.

As described above, according to the present embodiment, the following specific effects are obtained.
(1) In the reinitialization in the non-image area, the laser diode LD in which the slope η of the drive current Iη with respect to the light emission changes following the temperature change is also initialized in the non-image area (referred to as re-initialization). Thus, the drive current Iη can be set appropriately.
(2) Reinitialization is performed in readjustment when the electrical characteristics change due to the temperature characteristics of the laser diode LD after initialization. As a result, the light emission current and bias current (Isw, Iton, Itoff, etc.) of the semiconductor laser driving device can be appropriately reset according to the temperature characteristics of the laser diode LD.
(3) Reinitialization is intermittently performed by storing the reinitialization state (current values corresponding to the digital control signals SD2, SD3, SD4) in the register of the storage circuit 4.
(4) Reinitialization is performed in a plurality of times even in a short period where initialization is impossible, such as a non-image area. After completion of reinitialization, the user can reflect the reinitialization data automatically or reflect the completion signal after receiving the completion signal.

Embodiment 2. FIG.
FIG. 4 is a block diagram showing a configuration of a semiconductor laser driving apparatus according to Embodiment 2 of the present invention. The semiconductor laser driving device according to the second embodiment is different from the semiconductor laser driving device according to the first embodiment in FIG.
(1) A control circuit 14 is further provided.
(2) A reinitialization reflection signal Sinend_en and a reinitialization discard signal Sinend_dis are input to the control circuit 14 from the controller 20 of the image forming apparatus. In response to this, the control circuit 14 outputs a control signal S4 to the initialization circuit 3. The initialization circuit 3 executes an initialization process based on the control signal S4 in addition to the above signals.

  Here, when the reinitialization result reflection signal Sinend_en is input to the control circuit 14, the signal S 4 reflecting the reinitialization result is output to the initialization circuit 3. When the re-initialization result discard signal Sinend_dis is input to the control circuit 14, the signal S 4 for discarding the re-initialization result is output to the initialization circuit 3. Here, the re-initialization result reflection signal Sinend_en or the re-initialization result discard signal Sinend_dis can be set by the user at any timing or after receiving the initialization completion signal, for example, in the input unit connected to the controller 20 of the image forming apparatus. It is.

  FIG. 5 is a flowchart showing a reinitialization process executed by the initialization circuit 3 of the semiconductor laser driving device of FIG. In the semiconductor laser driving device of FIG. 4, for the sake of easy explanation, it is assumed that the initialization of the semiconductor laser diode LD is completed. The reinitialization process of FIG. 5 is the same as the process of steps S1 to S6, but the processes of steps S11 to S16 are different as follows, compared to the reinitialization process of FIG.

When the initialization is completed in step S3, the process proceeds to step S11.
(Step S11) The pulse of the initialization completion signal Sre_inend is output to the controller 20 of the image forming apparatus which is an external circuit to notify that the reinitialization is completed. And the process of step S12 and S14 is performed in parallel.
(Step S12) When the rising of the initialization reflection signal Sinend_en is detected, the process proceeds to S13. On the other hand, if not detected, the process returns to step S11.
(Step S13) The re-detected current set values Isw and Ithon are reflected in the bias current generation circuit 9 and the light emission current generation circuit 11 using the digital control signals SD2 and SD3, respectively, and the process proceeds to Step S16.
(Step S14) When the rising edge of the initialization discard signal Sinend_dis is detected, the process proceeds to S15. On the other hand, if not detected, the process returns to step S11.
(Step S15) The detected current setting values Isw and Iton are discarded from the storage circuit 4 and the process proceeds to Step S16.
(Step S16) The initialization completion signal Sre_inend is set to a low level, and the reinitialization process is terminated.

  FIG. 6 is a timing chart showing a reinitialization process of the semiconductor laser driving device of FIG. Here, FIG. 6A shows an example in which the control circuit 14 controls the reflection timing of the initialization result from the value of the initialization completion signal Sre_inend when the reinitialization result reflection signal Sinend_en changes from the low level to the high level. FIG. FIG. 6B shows an example of controlling the reinitialization to be forcibly started without reflecting the reinitialization result when the reinitialization result discard signal Sinend_dis changes from the low level to the high level. FIG.

  In FIG. 6, Si2 is a reinitialization signal, Ssw_d is a current setting value (register) of the light emission current generation circuit 11, and Sth_d is a current setting value (register) of the bias current generation circuit 9. Further, Sre_inend represents an initialization completion signal, Sinend_en represents a reinitialization result reflection signal, and Sinend_dis represents a reinitialization result discard signal. Note that the initial value of the current set value Ssw_d is c1, and the initial value of the current set value Sth_d is a1.

In FIG. 6A,
(T11) When the control signal Si2 becomes high level, a reinitialization state is established, and the initialization circuit 3 executes initialization processing. In the reinitialization state, the current setting values Ssw_d and Sth_d are sequentially updated according to the initialization.
(T12) When the control signal Si2 becomes a low level, the initialization circuit 3 interrupts the reinitialization process, writes the state at the time of interruption (current set value) to the storage circuit 4, and the values of the current set values Ssw_d and Sth_d are Return to c1 and a1, respectively.
(T13) When the control signal Si2 becomes high level again, the reinitialization process is resumed from the state where it was interrupted last time. Until the initialization is completed, the initialization circuit 3 repeats the reinitialization process at t111 to t13.
(T14) When the initialization process is completed, the initialization circuit 3 outputs an initialization completion signal Sre_inend at a high level.
(T15) Thereafter, the reinitialization process of t11 to t13 is not performed until the rising edge of the reinitialization result reflection signal Sinend_en or the reinitialization result reflection signal Sinend_dis is detected.
(T16) When the rising edge of the reinitialization result reflection signal Sinend_en is detected, the detected current setting values Ssw_d and Sth_d are reflected in the currents Isw and Iton (e1 and b1 in FIG. 6A).
(T17) The initialization completion signal Sre_inend becomes low level, and the process returns to t11.

In FIG. 6B, the same operation is performed from time t11 to t15.
(T18) When the rising edge of the reinitialization result discard signal Sinend_dis is detected, the detected current setting values Isw and Iton are discarded.
(T19) The initialization completion signal Sre_inend becomes low level, and the process returns to t11.

As described above, according to the present embodiment, the following specific effects are obtained.
(1) In the reinitialization in the non-image area, the laser diode LD in which the slope η of the drive current Iη with respect to the light emission changes following the temperature change is also initialized in the non-image area (referred to as re-initialization). Thus, the drive current Iη can be set appropriately.
(2) Reinitialization is performed in readjustment when the electrical characteristics change due to the temperature characteristics of the laser diode LD after initialization. As a result, the light emission current and bias current (Isw, Iton, Itoff, etc.) of the semiconductor laser driving device can be appropriately reset according to the temperature characteristics of the laser diode LD.
(3) Reinitialization is intermittently performed by storing the reinitialization state (current values corresponding to the digital control signals SD2, SD3, SD4) in the register of the storage circuit 4.
(4) Reinitialization is performed in a plurality of times even in a short period where initialization is impossible, such as a non-image area. After the reinitialization is completed, the reinitialization data is automatically reflected or the user can reflect or discard the reinitialization data at an arbitrary timing after receiving the completion signal.

Embodiment 3. FIG.
FIG. 7 is a block diagram showing a configuration of a semiconductor laser driving apparatus according to Embodiment 3 of the present invention. The semiconductor laser driving device according to the third embodiment is different from the semiconductor laser driving device according to the first embodiment in FIG.
(1) A control circuit 15 is further provided.
(2) A reinitialization reflection signal Sinend_en is input to the control circuit 15 from the controller 20 of the image forming apparatus. In response to this, the control circuit 15 outputs a control signal S4 to the initialization circuit 3. The initialization circuit 3 executes an initialization process based on the control signal S4 in addition to the above signals.

  Here, when the reinitialization result reflection signal Sinend_en is input to the control circuit 14, the signal S 4 reflecting the reinitialization result is output to the initialization circuit 3. Here, the re-initialization result reflection signal Sinend_en can be set by the user at an arbitrary timing or after receiving the initialization completion signal, for example, in the input unit connected to the controller 20 of the image forming apparatus.

  FIG. 8A is a flowchart showing a main routine of reinitialization processing executed by the initialization circuit 3 of the semiconductor laser driving device of FIG. FIG. 8B is a flowchart showing an interrupt process of the reinitialization process executed by the initialization circuit 3 of the semiconductor laser driving device of FIG. In order to facilitate the description of the reinitialization process, it is assumed that the initialization of the semiconductor laser diode LD has been completed. The re-initialization process of FIG. 8A is the same as the process of steps S1 to S6 as compared to the re-initialization process of FIG. 2, but the processes of steps S21 to S22 are different as follows.

In FIG. 8A,
(Step S21) The re-detected current set values Isw and Iton are held in the memory circuit 4.
(Step S22) The initialization completion signal Sre_inend is output at a high level for a predetermined period only for one pulse to notify the controller 20 of the image forming apparatus as an external circuit that the reinitialization is completed, and the process returns to step S2.

The interrupt process in FIG. 8B is executed when the reinitialization result reflection signal Sinend_en rises.
(S31) When the rising edge of the reinitialization result reflection signal Sinend_en is detected, the latest held current setting values Isw and Iton are reflected in the light emission current generation circuit 11 and the bias current generation circuit 9, respectively.

  FIG. 9 is a timing chart showing a reinitialization process of the semiconductor laser driving device of FIG. In FIG. 9, Si2 is a reinitialization signal, Ssw_d is a current setting value (register) of the light emission current generation circuit 11, Sth_d is a setting value (register) of the bias current generation circuit 9, Sre_inend is an initialization completion signal, and Sinend_en is a reconfiguration signal. An initialization result reflection signal is shown. Note that the initial value of the current set value Ssw_d is c1, and the initial value of the current set value Sth_d is a1.

In FIG. 9, the processing from time t11 to t15 is the same as that in FIG.
(T21) When the initialization process is completed, the initialization completion signal Sre_inend is output at a high level for one pulse for a predetermined period, the current setting value of the re-detection result is held in the storage circuit 4, and the re-initialization process is restarted. .
(T22) When the rising edge of the reinitialization result reflection signal Sinend_en is detected, the held current setting values Ssw_d and Sth_d are reflected in the current values Isw and Ithon (f1 and g1 in FIG. 9) of the latest detection results, respectively. Then, the initialization completion signal Sre_inend becomes low level, and the process returns to the process at time t11.

As described above, according to the present embodiment, the following specific effects are obtained.
(1) In the reinitialization in the non-image area, the laser diode LD in which the slope η of the drive current Iη with respect to the light emission changes following the temperature change is also initialized in the non-image area (referred to as re-initialization). Thus, the drive current Iη can be set appropriately.
(2) Reinitialization is performed in readjustment when the electrical characteristics change due to the temperature characteristics of the laser diode LD after initialization. As a result, the light emission current and bias current (Isw, Iton, Itoff, etc.) of the semiconductor laser driving device can be appropriately reset according to the temperature characteristics of the laser diode LD.
(3) Reinitialization is intermittently performed by storing the reinitialization state (current values corresponding to the digital control signals SD2, SD3, SD4) in the register of the storage circuit 4.
(4) Reinitialization is performed in a plurality of times even in a short period where initialization is impossible, such as a non-image area. After the reinitialization is completed, the reinitialization data is automatically reflected or after the completion signal is received, the user can reflect the reinitialization data at an arbitrary timing by the interrupt process of FIG. 8B.

Effects of the embodiment.
FIG. 10 is a graph showing the relationship between each current and the amount of light emission in the comparative example and the embodiment.

  The APC correction method according to the comparative example is a method for redetecting the threshold current Ith of the semiconductor laser, and is not a means for correcting the slope η of the drive current Iη with respect to the light emission amount. Also, if APC is performed in the non-image area when the slope η of the drive current Iη is reduced due to the temperature characteristics of the semiconductor laser, Iη> Isw. Here, Isw is a light emission current, and since an insufficient amount of the light emission current Isw is corrected by the bias current Iton, Ithon> Ith, and there is a possibility that light emission is always performed (see FIG. 10D). In the opposite case, Ith >> Ithon, and the response at the time of lighting becomes low. In addition, when the bias current Iton is sufficiently low to prevent light emission at all times, the response at the time of lighting is low. In addition, there is a means of performing initialization in order to re-detect the slope η of the drive current Iη. However, in many cases, the time required for completion of initialization cannot be taken between the paper and the non-image area.

  FIG. 10A shows the characteristics of the laser diode LD at room temperature. FIG. 10B shows the bias current Iton and the light emission current Isw after initialization. Further, FIG. 10C shows the characteristics of the laser diode LD when it is changed from room temperature to high temperature. FIG. 10D shows the light emission current Isw and the bias current Ithon corrected by APC. FIG. 10E shows the light emission current Isw and the bias current Ithon corrected by re-initialization according to the present embodiment.

  As described above, according to the embodiment of the present invention, as shown in FIG. 10E, the light emitting current and the bias current are obtained by performing reinitialization when the characteristics of the semiconductor laser change after initialization. Is appropriately reset according to the electrical characteristics of the semiconductor laser. Further, since the reinitialization state is stored in the storage circuit, the initialization (reinitialization) can be performed little by little in the non-image area. Further, by outputting the initialization completion signal, the user can freely select reflection or discard after confirmation.

1 ... comparison circuit,
3 ... initialization circuit,
4 ... Memory circuit,
5 ... Variable resistance,
7 ... Voltage divider circuit,
8 ... Drive current switch circuit,
9: Bias current generation circuit,
10: Bias current generation circuit,
11: Light emission current generation circuit,
12 ... Auxiliary current generation circuit,
13 ... selection circuit,
14, 15 ... control circuit,
16 ... Or gate,
20 ... Controller of the image forming apparatus,
LD: Semiconductor laser diode (laser diode),
PD: Photodiode.

JP 2004-153118 A

Claims (7)

In a semiconductor laser driving apparatus for controlling the current supplied to the semiconductor laser so that a desired light emission amount can be obtained by the initialization process, and controlling the driving of the semiconductor laser,
An initialization circuit that divides the initialization process in a plurality of non-image areas;
A storage circuit for storing a current setting value of a bias current and a light emission current when the initialization process is interrupted,
The initialization circuit includes:
When the initialization signal becomes valid, the initialization process starts.
When the initialization signal becomes invalid during the initialization process, the initialization process is interrupted, and the current setting values of the bias current and the light emission current at the interruption of the initialization process are stored in the storage circuit. Then, when the initialization signal becomes valid, the current setting value at the time of interruption is read and set from the storage circuit, and the initialization process is restarted from the state at the time of interruption. Semiconductor laser drive device. The non-image area is
(A) a period from an end synchronization signal of a certain main scanning line to a start synchronization signal of the next main scanning line;
2. The image processing apparatus according to claim 1, wherein (B) is at least one of a section from an end synchronization signal of the last main scanning line of the paper on which an image is formed to a start synchronization signal of the first main scanning line of the next paper. Semiconductor laser drive device. The semiconductor laser driving device comprises:
A first bias current generation circuit that generates a desired first bias current lower than an oscillation threshold current of the semiconductor laser and constantly outputs the first bias current to the semiconductor laser;
A second bias current generation circuit that generates a second bias current for causing the semiconductor laser to emit light in accordance with an input signal and outputs the second bias current to the semiconductor laser;
A light emission current generating circuit that detects a light emission amount of the semiconductor laser, generates a light emission current so that the light emission amount becomes a desired value, and outputs the light emission current to the semiconductor laser;
An auxiliary current generation circuit that generates a predetermined auxiliary current and outputs the generated auxiliary current to the semiconductor laser;
The initialization circuit executes an initialization process for detecting a light emission characteristic of the semiconductor laser, and outputs a signal indicating a current value of the second bias current obtained from the detected light emission characteristic to the second bias. Output to the current generator,
The initialization circuit emits a signal indicating a current value of the light emission current so that a light emission amount of the semiconductor laser by a sum current of the second bias current, the light emission current, and the auxiliary current becomes a desired value. 3. The semiconductor laser driving device according to claim 1, wherein the semiconductor laser driving device outputs the current to a current generating circuit.   The initialization circuit sets the second bias current and light emission current setting values stored in the storage circuit after completion of the initialization process, respectively, to the second bias current generation circuit and the light emission current generation circuit. 4. The semiconductor laser driving device according to claim 3, wherein the output is controlled so as to be reflected in the output.   The initialization circuit outputs an initialization completion signal to an external circuit upon completion of the initialization process, and in response thereto, when a reinitialization result reflection signal is input from the external circuit, the storage circuit Are controlled so that the second bias current and the light emission current set value stored in the output are reflected in the second bias current generation circuit and the light emission current generation circuit, respectively, and output from the external circuit. 4. The semiconductor laser according to claim 3, wherein when the initialization result discard signal is input, control is performed so as to discard the current setting values of the second bias current and the light emission current stored in the storage circuit. Drive device.   The initialization circuit stores the current setting values of the bias current and the light emission current at the time of interruption of the initialization process in the storage circuit upon completion of the initialization process, and then outputs an initialization completion signal to an external circuit Then, when the reinitialization result reflection signal is input from the external circuit in the interrupt process in response to the initialization process, the second bias current stored in the storage circuit and 4. The semiconductor laser driving device according to claim 3, wherein a current setting value of the light emission current is controlled to be reflected and output to the second bias current generation circuit and the light emission current generation circuit, respectively. In a semiconductor laser driving method for a semiconductor laser driving device for controlling driving of the semiconductor laser by controlling a current supplied to the semiconductor laser so that a desired light emission amount can be obtained by initialization processing,
The semiconductor laser driving device comprises:
An initialization circuit that divides the initialization process in a plurality of non-image areas;
A storage circuit for storing a current setting value of a bias current and a light emission current when the initialization process is interrupted,
The initialization circuit starts the initialization process when an initialization signal becomes valid; and
When the initialization signal becomes invalid during the initialization process, the initialization circuit interrupts the initialization process, and current setting values of the bias current and the light emission current when the initialization process is interrupted Is stored in the memory circuit, and when the initialization signal becomes valid, the current setting value at the time of interruption is read from the memory circuit and set, and the initialization process is resumed from the state at the time of interruption. A semiconductor laser driving method comprising the steps of:

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