JP5034986B2 - Surface emitting laser drive device - Google Patents

Description

  The present invention relates to a surface emitting laser driving device, and more particularly to a surface emitting laser driving device suitable for use in laser xerography.

  In the conventional edge-emitting laser, a current drive circuit has generally been used as shown in FIG. This current drive circuit supplies the current generated in the constant current circuit constituted by the amplifier 5, the transistor Ql, and the resistor RE1 shown in the figure to the laser LD1 by turning on / off the current switches Q2 and Q3. The reason why this current driving circuit has been used conventionally is as follows.

  As shown in FIG. 38, in the edge-emitting laser, the driving current increases exponentially with respect to the applied voltage, so that when the voltage is controlled, the differential resistance (ΔV / ΔI) varies depending on the bias point, A non-linear element enters the negative feedback loop for control, making control difficult. On the other hand, when driven by current, the amount of light is proportional to the current above the laser oscillation threshold current, so the negative feedback loop is composed of linear elements and control is facilitated. Further, even when a large number of lasers must be driven, a current source can be provided for each laser relatively easily if current driving is performed.

  Unlike the voltage drive circuit, the current drive circuit shown in FIG. 39 has no means for shortening the time constant. For this reason, it is generally used to superimpose a differential current.

  For example, in the laser diode drive control circuit shown in FIG. 2 of Patent Document 2, when the signal Vs becomes high, the transistor Q3 is turned on, and the base of Q4 is driven with a time constant determined by the capacitor C and the resistor R1. The differential current corresponding to Vs shown in FIG. 5 of Patent Document 2 from the transistor Q4 compensates for the rise of the laser. In this laser diode drive control circuit, since the magnitude of the differential current is not controlled in accordance with the operating state, for example, when the laser light amount is changed, the temperature is changed, or the drive current is changed due to the change of the laser over time. There is a problem that the compensation amount is excessive or insufficient.

On the other hand, there is a semiconductor light emitting element driving circuit connected to the speed-up capacitor in parallel with the resistor for current adjustment to record over THE. Then, it generates a drive current waveform of O over-shoot Gimi obtain a rectangular light output. The semiconductor light emitting element driving circuit, the amplitude of the output voltage is also increased amplitude of the differential current waveform increases, because V-I characteristics of the laser diode is nonlinear, all of the light amount at the same capacitor capacity It cannot be corrected.

The light emitting element driving circuit shown in FIG. 1 of Patent Document 3, as shown in FIG. 2 of Patent Document 3, the laser turned on, a pulse waveform that matches the off generated by Rd, speed-up capacitor the terminal voltage Thus, the differential current Id is superimposed by capacitively coupling to the laser. This light emitting element driving circuit applies a complementary current to be supplied to the laser as a current to be supplied to the resistor Rp that generates a rectangular wave. Therefore, the differential current superimposed in proportion to the drive current to the laser changes. Similar to FIG. 3 of Patent Document 4 , this semiconductor light emitting element driving circuit also has a problem that even if correction can be performed under certain conditions due to the nonlinearity of the diode, the correction is shifted when the conditions change.

Further, except for FIG. 3 of Patent Document 4 , the circuit configuration of the differential current generating circuit and the laser driving circuit are different, and therefore the phase of the differential current and the phase of the driving current may be shifted. Further, when the phase is shifted, another problem occurs such that the rising becomes two stages.
JP 57-13790 A JP 62-62572 A JP-A-9-83442 JP-A-57-39593

  Here, the reason why the correction is shifted when the VI characteristic of the laser is nonlinear will be described.

  FIG. 40 is a diagram illustrating a circuit configuration of Vcsel constant current driving. This Vcsel constant current drive circuit includes a current source for driving a laser, a pulse voltage source for generating a pulse whose amplitude is proportional to the current value of the current source and synchronized with a laser on / off control switch, And a capacitor for superimposing the differential current on the driving current of the laser.

  For example, when the laser drive current is doubled, the differential current for correction is also doubled. FIG. 41 is a diagram showing the VI characteristics of the semiconductor laser. According to this VI characteristic, even if the current is doubled, the terminal voltage increases only slightly because the VI characteristic is exponential. If the rounding of the rise due to the parasitic capacitance of the wiring is corrected, the differential current must be set in proportion to this change in voltage. However, since it is proportional to the drive current, if the laser drive current is doubled, the differential current is also doubled, resulting in overcompensation.

  On the contrary, as shown in FIG. 42, when the laser drive current is halved as shown from left to right, the applied voltage of the laser changes only slightly. On the other hand, since the compensation differential current is reduced to half, the compensation is insufficient and the waveform is distorted. In laser xerography, the laser power is constantly controlled in accordance with the environment and deterioration of the photosensitive member, and it is fatal that it can be used only with a constant light amount.

  Accordingly, an object of the present invention is to provide a surface emitting laser driving apparatus that compensates for an optimal state even if a change occurs in the current flowing through the surface emitting laser and suppresses power fluctuation of the surface emitting laser.

First aspect of the present invention, a surface emitting laser for outputting a laser beam, a current source for supplying a current to the surface emitting laser when on the surface emitting laser, the pulsed voltage supplied to the surface emitting laser controls the voltage level, a pulse voltage the controlled in synchronization with oN of the surface emitting laser and a pulsed voltage supply means for supplying to the surface emitting laser, the pulsed voltage supply means, the surface emitting laser Is acquired and held when the terminal voltage of the surface emitting laser is substantially converged and is turned on, and the terminal voltage of the surface emitting laser when the surface emitting laser is turned on and started is held. The voltage level is controlled to match the converged terminal voltage .

The present invention is a current drive type in which a predetermined current is further supplied when the surface emitting laser is turned on. Parasitic capacitance exists in the wiring from each circuit to the surface emitting laser, and this causes rounding of the waveform. For this reason, a pulse voltage is supplied to the surface emitting laser in synchronization with the on / off of the surface emitting laser. However, when the current flowing through the surface emitting laser changes, so-called overshoot or undershoot occurs. Therefore, in order to correct the combined pulse voltage to the change, and controls the voltage level of the pulse voltage. In order to eliminate such overshoot and undershoot, the current value of the bias current may be controlled as in the ninth or thirteenth aspect .

The present invention, when supplying a pulse voltage to a surface-emitting laser in synchronism with the ON of the surface-emitting laser, by controlling the bias current to control the voltage level of the pulse voltage, the change in current flowing through the surface-emitting laser Even if this occurs, it can be compensated in an optimum state, and the power fluctuation of the surface emitting laser can be suppressed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, a characteristic basic configuration of each apparatus will be described, and then a configuration of a plurality of channels (multi-lasers) will be described.

1. Basic Configuration (1) Voltage Drive Type The voltage drive type surface emitting laser driving device according to the present embodiment supplies a voltage source with a current output complementarily to the drive current of the surface emitting laser. Suppresses load fluctuations.

  As shown in FIG. 1, the surface emitting laser driving device includes a terminal resistor R4 and a capacitor C1 connected in series, and a surface emitting laser LD connected in parallel therewith. The cathode side of the surface emitting laser LD and the other end of the capacitor C1 are grounded.

  Further, the surface emitting laser driving device is connected in parallel with a bias current source Ib that supplies current to the anode side of the surface emitting laser LD and the termination resistor R4, and a complementary current source Is that outputs current via the switch SW1. A complementary current source Is ′ for supplying current to the resistor R1 and the capacitor C2, a current source Ia whose input side is connected to the switch SW2, and voltage regulators (voltage sources) V1 and V2.

  The switch SW1 outputs the complementary current Is from the complementary current source Is via the terminal a or the terminal b. The terminal a of the switch SW1 is connected to the terminal a of the switch SW2, and the terminal b is connected to the anode side of the surface emitting laser LD.

  One end of the resistor R1 and the capacitor C2 is connected to the output side of the complementary current source Is', and the other end thereof is grounded. Note that the terminal voltage of the capacitor C2 becomes the control voltage of the current source Ia.

  The terminal a of the switch SW2 is grounded through the resistor R2. The resistor R2 is for constantly flowing out current so that it can be used even in a source type power supply regulator. The terminal b of the switch SW2 is grounded via the resistor R3. The switch SW2 outputs a current from the terminal a or the terminal b. The input side of the current source Ia is connected to the terminal a or the terminal b of the switch SW2, and its output side is grounded.

  The voltage source V1 applies a voltage V1 to the other end of the grounded resistor R3. The voltage source V2 is connected in series with the resistor R4, connected to the other end of the grounded capacitor C1, and further connected to the other end of the grounded resistor R2, and applies the voltage V2. The capacitor C1 has a role of suppressing an increase in output impedance at a high frequency. The capacitor C3 holds the control voltage of the complementary current source Is, and the capacitor C4 holds the control voltage of the bias current source Ib.

  In the surface emitting laser driving apparatus configured as described above, the bias current Ib output from the bias current source Ib branches and flows through the termination resistor R4 and the surface emitting laser LD.

  When the surface emitting laser LD is turned on, the switch SW1 is switched to the terminal b. The complementary current Is output from the complementary current source Is flows into the termination resistor R4 and the laser LD via the switch SW1. Thereby, the surface emitting laser LD is turned on. At this time, the current flowing through the termination resistor R4 also increases, and the amount of the complementary current Is flowing through the termination resistor R4 causes the load fluctuation of the voltage source V2.

  Therefore, when the surface emitting laser LD is turned off, the switch SW1 is switched to the terminal a, and the complementary current Is is directly supplied to the voltage source V2. Thereby, the magnitude of the current supplied to the voltage source V2 can be made substantially equal regardless of whether the surface emitting laser LD is turned on or off.

  However, when all of the complementary current Is is passed through the resistor R2, since the shunt to the surface emitting laser LD is not taken into account, the compensation is excessive, and the potential of the voltage source V2 changes in the reverse direction. Therefore, in synchronization with the on / off of the surface emitting laser LD, a shunt current to the surface emitting laser LD is corrected by another current source.

  As shown in FIG. 2, when the terminal voltage of the surface emitting laser LD increases, the terminal voltage-current characteristic becomes a linear region. The slope at that time is the reciprocal of the parallel combined resistance of the termination resistance Rsh and the internal resistance Rld of the laser. Since the termination resistance Rsh and the internal resistance Rld are substantially constant, the ratio of the current flowing through the termination resistance Rsh and the current flowing through the surface emitting laser LD is constant in the linear region.

  Here, Equation (1) representing the current flowing through the resistor R2 when the surface emitting laser LD is on and Equation (2) representing the current flowing through the resistor R2 when the surface emitting laser LD is off are shown.

(Current of R2 when LD is on) = α × (Is + Ib) (1)
(Current of R2 when LD is off) = α × Ib + Is−Ia (2)
Further, the correction current Ia is set to be proportional to the mirror complementary current Is ′ of the complementary current Is. That is, it sets like Formula (3).

Ia = Is × (1−α) (3)
α indicates the current shunt ratio of the termination resistor R4 and the surface emitting laser LD, and can be adjusted by changing the value of the resistor R1. Substituting equation (3) into equation (2) matches equation (1). That is, if the correction current Ia is set in proportion to the complementary current Is, the load of the voltage source V2, that is, the output voltage can be made constant regardless of whether the surface emitting laser LD is on or off.

  Although the shunt ratio α is constant, when the current flowing through the surface emitting laser LD is small, an exponential function is included, and therefore the shunt ratio α cannot be regarded as a constant. In such a case, the current flowing through the termination resistor R4 is calculated from the difference between the potential of outp and the potential of the voltage source V2, and the difference current between this current and the mirror complementary current Is ′ of Is is set as the correction current Ia. You can also. At this time, even if the surface emitting laser LD operates in the exponential function region, the load of the voltage source V2 does not fluctuate.

  Next, the surface emitting laser driving device shown in FIG. 3 will be described. Here, the switches SW1 to SW3 are switched in conjunction with each other. FIG. 3 shows the state of the switches SW1 to SW3 when the surface emitting laser LD is on.

  When the surface emitting laser LD is turned off, the switch SW3 is turned on. The operational amplifier A1 supplies a control voltage to the current source Ildd connected to the resistor R5 so that the terminal voltage of the resistor R5 is equal to the terminal voltage of the termination resistor R4.

  The current source Ildd 'forms a current mirror with the current source Ildd. The current source Ildd 'operates to subtract a current proportional to the terminal voltage of the resistor R4 from the source complementary current Is' of the complementary current source Is'. Accordingly, by adjusting the gains of the current source Ildd and current source Ildd 'and the resistance value of the resistor R5, the current source Ildd' sinks a current corresponding to the current flowing through the termination resistor R4. As a result, a current corresponding to the current flowing through the surface emitting laser LD out of the complementary current Is ′ flows into the resistor R1.

  When the correction current Ia is subtracted from the complementary current Is, the amount of the complementary current Is that has flowed to the surface emitting laser LD when the surface emitting laser LD is turned on is subtracted, and only the amount that has flowed to the termination resistor R4. It flows to the resistor R2. As a result, the current flowing through the resistor R2 is always constant even if the surface emitting laser LD is on / off because the VI characteristic of the surface emitting laser LD is in a non-linear region. Therefore, it is possible to prevent the output of the voltage source V2 from fluctuating due to load fluctuations.

(2) Current Drive Type As shown in FIG. 4, the current drive type surface emitting laser driving device turns on the surface emitting laser LD and the bias current source Ib that constantly supplies the bias current Ib to the surface emitting laser LD. A switch SW, a complementary current source Is for supplying a current to the surface emitting laser LD via the switch SW, and a pulse generator VP for performing compensation are provided.

  A parasitic capacitance Cst generally exists in the wiring from each circuit to the surface emitting laser LD, and this parasitic capacitance Cst causes a waveform rounding. The pulse generator VP generates a pulse signal Vpulse in synchronization with the on / off of the switch SW, and supplies this to the laser LD through the speed-up capacitor Cs. This compensates for the rising edge due to the parasitic capacitance Cst.

  Unless the compensation amount is optimized, overshoot and undershoot occur as shown in FIG. The voltage amplitude at the time of rising is determined by the voltage ratio of the voltage of the pulse signal Vpulse × capacitance Cs and the parasitic capacitance Cst, and is Vpulse × Cs / (Cs + Cst).

  When the surface emitting laser LD is on in a steady state, the terminal voltage of the surface emitting laser LD is determined from the voltage-current characteristics of the laser as shown in FIG. A bias current Ib and a complementary current Is flow through the surface emitting laser LD, and the terminal voltage of the surface emitting laser LD becomes (Vb + Vs).

  When the surface emitting laser LD is off, only the bias current Ib flows through the surface emitting laser LD, and the terminal voltage of the surface emitting laser LD at this time is Vb. Accordingly, the compensation condition is that the voltage amplitude at the time of rising and the potential difference between the laser on and the laser off in the steady state are equal, and therefore the following equation is satisfied.

Vpulse × Cs / (Cs + Cst) = (Vb + Vs) −Vb = Vs
In order to satisfy the above equation, which is a compensation condition, it is preferable to control Vpulse or other steady-state potential.

  The Vpulse control can be realized easily on the circuit by changing the high level of the pulse signal, and there is no adverse effect due to the correction. If a compensation circuit for each surface emitting laser LD is provided, a voltage source having a low output impedance for Vpulse is required, so this method is suitable for collective control of all the surface emitting lasers LD. In other steady state potential control (Vs control), (Vb + Vs) is determined by APC, so Vb may be controlled. It is practical because it is easy to control the bias current for each laser. However, if the bias is lowered too much, it causes a harmful effect and is suitable for fine adjustment for each channel ch.

  FIG. 7A is a diagram illustrating a case where the compensation amount is controlled by Vpulse. There is an overshoot before control. After the adjustment, the terminal voltage when the surface emitting laser LD in the steady state is on and the terminal voltage when the surface emitting laser LD is off do not change, and there is no overshoot. FIG. 7B is a diagram showing a case where the compensation amount is controlled by the bias current Ib. There is an overshoot before control. When adjusted with the bias current Ib, the terminal voltage when the surface-emitting laser LD is off is lowered, thereby eliminating the overshoot.

(Vpulse control)
In order to eliminate such overshoot, the surface emitting laser driving device includes amplifiers A1 and A2, a bias current source Ib, and a complementary current source Is as shown in FIG.

  The bias current source Ib outputs a bias current Ib according to the control voltage from the variable voltage source Vb, and supplies this bias current Ib to the anode side of the surface emitting laser LD. The complementary current source Is has a control voltage set by the variable voltage source Vs and supplies the complementary current Is to the switch SW3. The switch SW3 supplies the complementary current Is to the surface emitting laser LD when the terminal a is selected, and outputs the complementary current Is to the outside when the terminal b is selected.

  One input terminal of the amplifier A1 is connected to the anode side of the surface emitting laser LD via the switch SW1. One end of the capacitor C5 is connected between the amplifier A1 and the switch SW1, and the other end is grounded. The other input terminal of the amplifier A1 is connected to the anode side of the surface emitting laser LD.

  One input terminal of the amplifier A2 is connected to the output terminal of the amplifier A1. The other input terminal of the amplifier A2 is connected to the output terminal of the amplifier A2. Further, the output terminal of the amplifier A2 is connected to one end of the capacitor C2. The other end of the capacitor C2 is grounded. Furthermore, one end of the capacitor C2 is connected to the terminal a of the switch SW2, and the other end is connected to the terminal b of the switch SW2. The switch SW2 supplies the pulse signal Vpulse from the terminal a or the terminal b to the anode side of the surface emitting laser LD via the capacitor C1.

The surface emitting laser driving apparatus configured as described above, to turn fraud and mitigating risk switch SW1 at the time t 2 shown in FIG. 9 (A). As a result, the capacitor C5 holds the terminal voltage V2 of the surface emitting laser LD. Note that the switches SW2 and SW3 select the terminal a .

At time t1 to t2 immediately after the switches SW2 and SW3 are switched to the terminal a and the terminal voltage of the surface emitting laser LD rises, the amplifier A1 outputs a pulse signal so that the voltage from time tl to t2 matches the voltage V2. Negative feedback control is performed on the potential of Vpulse (voltage of C2).

  After the voltage V1 matches the voltage V2, the switch SW2 is switched to the terminal b. As a result, the capacitor C2 holds the voltage at that time and automatically sets the Vpulse voltage. Of course, the control is not completed with one pulse, so that the pulse signal Vpulse is converged continuously by such adjustment.

  As described above, the surface emitting laser driving device can automatically set the voltage of the pulse signal Vpulse to the capacitor C2 even if the bias current Ib and the complementary current Is change to change the power of the surface emitting laser LD. Therefore, it can compensate so that it may always be in an optimal state.

(Bias control)
As shown in FIG. 10, the surface emitting laser driving device that performs bias control includes a bias current source Ib that constantly outputs a bias current Ib, a complementary current source Is, and amplifiers A1 and A2.

  The bias current source Ib outputs a bias current Ib according to the control voltage from the amplifier A1, and supplies the bias current Ib to the anode side of the surface emitting laser LD. The complementary current source Is has a control voltage set by the variable voltage source Vs and supplies the complementary current Is to the switch SW4. The switch SW4 supplies the complementary current Is to the surface emitting laser LD when the terminal a is selected, and outputs the complementary current Is to the outside when the terminal b is selected.

  One input terminal of the amplifier A2 is connected to the constant voltage source Vpulse. The other input terminal is connected to the output terminal of the amplifier A2. Further, the output terminal of the amplifier A2 is connected to one end of the capacitor C3. Note that the other end of the capacitor C3 is grounded. Furthermore, one end of the capacitor C3 is connected to the terminal a of the switch SW3, and the other end is connected to the terminal b of the switch SW3. The switch SW3 supplies the pulse signal from the terminal a or the terminal b to the anode side of the surface emitting laser LD via the capacitor C2.

  One input terminal of the amplifier A1 is connected to the anode side of the surface emitting laser LD. The other input terminal is connected to the anode side of the surface emitting laser LD through the switch SW1. A capacitor C1 is connected between the other input terminal of the amplifier A1 and the switch SW1. The other side of the capacitor C1 is grounded.

In the surface emitting laser driving device configured as described above, at time t2 shown in FIG. 9B, the switch SW1 is turned on and the potential V2 is held in the capacitor C1. Note that the switches SW3 and SW4 select the terminal a .

Next, when the switches SW2 and SW3 are switched to the terminal a, the pulse signal Vpulse rises. The amplifier A1 performs negative feedback control so that the voltage of the surface emitting laser LD at that time coincides with the held voltage V2. Here, since the constant voltage source Vpulse outputs a fixed voltage, the compensation is optimized if the terminal voltage of the surface emitting laser LD is controlled when the surface emitting laser LD is off.

  Since this surface emitting laser driving device does not require a constant voltage power source with low output impedance, it can be integrated into an IC and provided for each channel. Therefore, it is suitable for fine adjustment of the surface emitting laser LD individually.

  These surface emitting laser driving devices determine the compensation amount from the waveform shape of the terminal voltage of the surface emitting laser LD. However, when the internal resistance of the surface-emitting laser LD is small, even if the surface-emitting laser LD is turned on / off, the change in the terminal voltage is small and it may be difficult to control. Further, reproducibility may be insufficient with only the terminal voltage of the surface emitting laser LD due to other factors such as temperature fluctuation. In such a case, it is also possible to control with the light amount monitor signal of the surface emitting laser LD.

(Vpulse control using light intensity)
Such a surface emitting laser driving apparatus is configured as shown in FIG. Specifically, the surface-emitting laser driving device uses a bias current source Ib that supplies a bias current Ib to the surface-emitting laser LD, a complementary current source Is, amplifiers A1, A2, and A3, and light amounts of the surface-emitting laser LD. And a photodiode PD for detection.

  The bias current source Ib outputs a bias current Ib according to the control voltage from the variable voltage source BIASREF, and supplies the bias current Ib to the anode side of the surface emitting laser LD. The complementary current source Is outputs the complementary current Is through the switch SW1 according to the control voltage from the amplifier A1, and supplies it to the switch SW4. The switch SW4 supplies the complementary current Is to the surface emitting laser LD when the terminal a is selected, and outputs the complementary current Is to the outside when the terminal b is selected.

  A voltage Vcc is applied to the cathode side of the photodiode PD. The anode side of the photodiode PD is connected to a resistor Rpd and a capacitor Cst connected in parallel.

  One input terminal of the amplifier A1 is connected to the anode side of the photodiode PD. The other input terminal of the amplifier A1 is connected to a voltage source APCREF that outputs the APC reference voltage V_APCREF. The amplifier A1 sets the control voltage of the complementary current source Is so that the voltage detected by the photodiode PD becomes the reference voltage V_APCREF. The two input terminals of the amplifier A3 are similarly connected. One input terminal of the amplifier A2 is connected to the output terminal of the amplifier A3 via the switch SW2. In addition, the connection relationship of the amplifier A2, the capacitor C2, and the switch SW3 is substantially the same as that in FIG. However, the switch SW3 is connected to the anode side of the surface emitting laser LD via the capacitor Cs. In FIG. 11, only one channel ch is shown, but the other channel ch is configured similarly.

  By the way, if the adjustment of Vpulse is not successful and as shown in FIG. 12 (A), the average light quantity of the surface emitting laser LD is automatically turned on by continuously lighting one laser when overcompensated. The amount of overshoot is added to the reference voltage V_APCREF of the monitor light amount at the time, and the monitored light amount increases. As shown in FIG. 12B, when the compensation amount is insufficient, undershoot occurs, and the amount of light of the surface emitting laser LD becomes lower than the voltage V_APCREF.

  Therefore, in this surface emitting laser driving apparatus, a plurality of surface emitting lasers LD are alternately turned on to always emit only one light. The amplifier A3 controls the output of the amplifier A2, that is, Vpulse so that the voltage detected by the photodiode PD becomes the voltage V_APCREF. When the voltage detected by the photodiode PD matches V_APCREF, compensation is performed in an optimum state.

(Bias control using light intensity)
A surface-emitting laser driving device that performs bias control using the amount of light is configured as shown in FIG. In addition, since there exists a part of the same structure as FIG. 11, description of the location is abbreviate | omitted.

  Since the amplifier A2 has one input terminal connected to the compensation voltage source REF and the other input terminal connected to the output terminal, the amplifier A2 outputs a predetermined Vpulse. The amplifier A3 compares the voltage V_APCREF, which is a fixed value, with the voltage detected by the photodiode PD, and supplies a control voltage to the bias current source Ib via the switch SW2 so that they match. FIG. 13 shows only the channel ch1, but the other channels ch are similarly configured. Furthermore, the state showing overcompensation and undercompensation is the same as in FIG.

  In the surface emitting laser driving apparatus configured in this way, the ripple component is averaged and controlled by increasing the switching frequency of the surface emitting laser LD to such an extent that the outputs of the operational amplifiers A1, A2, A3 and the photodiode PD do not respond. The accuracy can be increased. Further, when there is little variation in the compensation amount between the channel channels, the compensation amount can be controlled collectively by turning on the surface emitting laser LD in turn for each channel channel.

(Individual control by Vpulse)
The surface-emitting laser driving device shown in FIGS. 11 and 13 is suitable for collectively controlling a plurality of surface-emitting lasers LD, and optimizing the compensation amount of each surface-emitting laser LD. Can not. Hereinafter, optimization of the compensation amount of each surface emitting laser LD will be described.

  The surface emitting laser driving apparatus that individually controls the surface emitting laser LD with Vpulse is configured as shown in FIG. The configuration is the same as in FIG. 11 except for the connection relationship of the input terminal of the amplifier A3.

  One input terminal of the amplifier A3 is connected to the anode side of the photodiode PD as in FIG. A voltage obtained by dividing the voltage V_APCREF by the resistors R1 and R2, that is, [R2 / (R1 + R2)] V_APCREF is input to the other input terminal of the amplifier A3.

  In the surface emitting laser driving apparatus configured as described above, one surface emitting laser LD is pulse-lit as shown in FIG. At this time, if there is a parasitic capacitance Cst in parallel with the load resistor Rpd of the photodiode PD and the lighting frequency of the surface emitting laser LD is high, the photodiode PD outputs a voltage that is an averaged light amount monitor signal.

  The amplifier A3 compares this output voltage with the voltage obtained by dividing the reference voltage V_APCREF in the automatic light quantity control by the resistors R1 and R2, and performs negative feedback control on Vpulse. Here, the voltage division ratio of the reference voltage V_APCREF is preferably determined by the duty of pulse lighting of the surface emitting laser LD. For example, when the photodiode PD is turned on with a duty of 50%, the resistors R1 and R2 are determined so that half of the voltage V_APCREF becomes the input voltage of the operational amplifier A3. As a result, when Vpulse is optimized, the light amount monitor signal matches the voltage of V_APCREF / 2.

(Individual control by bias current)
Similarly, a surface emitting laser driving apparatus that controls each surface emitting laser LD with a bias current is configured as shown in FIG. In the case of overcompensation and insufficient compensation, the waveform diagram is the same as FIG.

  The amplifier A3 shown in FIG. 16 compares the voltage detected by the photodiode PD with the voltage obtained by dividing the reference voltage V_APCREF in the automatic light quantity control by the resistor R1 and the resistor R2, and determines the control voltage of the bias current source Ib. Set. Here, the voltage division ratio is preferably determined by the pulse lighting duty of the surface emitting laser LD, as in the above description.

(Open loop control)
Each of the surface emitting laser driving devices described above performs highly accurate negative feedback control. A single mode surface emitting laser has a high internal resistance and a linear voltage-current characteristic. Therefore, by utilizing this feature, a certain amount of compensation can be controlled even in open loop control.

  For example, the surface emitting laser driving device shown in FIG. 17 controls the compensation amount Vpulse with reference to the complementary current Is.

  As a premise, the bias current source Ib is set with a bias current Ib when the surface emitting laser LD is forward-biased and the current starts to increase rapidly. When the complementary current Is is superimposed on the bias current Ib, the terminal voltage of the surface emitting laser LD also increases in proportion to the increase in the complementary current Is. At this time, the current generated by the current mirror circuit of the complementary current source Is is supplied to the resistor VR1, and a terminal voltage proportional to the complementary current Is is generated in the resistor VR1. The amplifier A2 controls Vpulse using the terminal voltage of the resistor VR1. Therefore, the complementary current Is superimposed on the bias current Ib is proportional to the voltage amplitude. Accordingly, appropriate correction can be performed in accordance with the light amount of the surface emitting laser LD by appropriately selecting the value of the resistor VR1.

  The bias current Ib is set to a current at which the surface emitting laser LD is forward-biased. After the surface emitting laser LD is forward-biased as described above, the voltage-current characteristic becomes linear. As a result, for example, when the complementary current Is is halved, as shown in FIG. 18, for example, the amplitude of the terminal voltage of the surface emitting laser LD is also halved. Therefore, the compensation amount can always be in an optimum state without performing feedback.

  What is common in the above description is that a double-throw analog switch is used to generate the pulse signal Vpulse. If a CMOS process is used, this switch can have the same configuration and the same signal as the current switch SW4 of the complementary current source. For this reason, compared with the case where bipolar is used, waveform distortion due to delay caused by a different circuit configuration can be suppressed.

(3) Automatic light quantity control Next, automatic light quantity control that shortens the convergence time of the first laser and further suppresses output fluctuation of the comparator that occurs when the channel ch is switched will be described.

  As shown in FIG. 19, the surface emitting laser driving apparatus that performs such automatic light quantity control includes n surface emitting lasers LD1 to LDn, and n complementary current sources Is1 to Isn that supply currents to the lasers. , An operational amplifier OP1 for setting a control voltage to be supplied to each of the complementary current sources Is1 to Isn, a photodiode PD for detecting the light quantity of each of the surface emitting lasers LD1 to LDn, and an operational amplifier OP2.

  The input sides of the complementary current sources Is1 to Isn are connected to the power supply voltage 5V. The output side of each complementary current source Is1 to Isn is connected to the anode side of the surface emitting lasers LD1 to LDn via the switches S1 to Sn. The cathode sides of the surface emitting lasers LD1 to LDn are grounded.

  The output side of the operational amplifier OP1 is connected to the switches SW1 to SWn. The switches SW1 to SWn supply control voltages to the complementary current sources Is1 to Isn through the amplifiers A1 to An, respectively. The non-inverting input terminal of the operational amplifier OP1 is connected to the constant voltage source Vref. The inverting input terminal of the operational amplifier OP1 is connected to the output terminal of the operational amplifier OP1 through the capacitor C2, and is also connected to the amplifier AZ through the switch SWAPC1.

  A power supply voltage of 5 V is applied to the cathode side of the photodiode PD. The anode side of the photodiode PD is grounded via a resistor R, is connected to the inverting input terminal of the operational amplifier OP1 via the amplifier AZ and the switch SWAPC1, and is further connected to the switch SWAPC2.

  The terminal a of the switch SWAPC2 is connected to the output terminal and the inverting input terminal of the operational amplifier OP2. The terminal b of the switch SWAPC is connected to the non-inverting input terminal of the operational amplifier OP. Note that one end of the capacitor C1 is connected to the non-inverting input terminal of the operational amplifier OP2, and the other end is grounded.

  In the surface emitting laser driving apparatus configured as described above, the switch SWAPC1 is turned on and the switch SWAPC2 is switched to the terminal b during automatic light quantity control.

  At this time, the operational amplifier OP1 compares and detects an error between the monitor voltage output from the amplifier AZ and the reference voltage Vref. At this time, the capacitor C1 inserted in the negative feedback loop is charged with a voltage difference between the output terminal and the inverting input terminal of the operational amplifier OP1. At the same time, the capacitor C2 is charged by the terminal voltage of the resistor R, that is, the output voltage of the photodiode PD subjected to current-voltage conversion.

  At the end of the automatic light amount control, the switch SWAPC1 is in a high impedance state, that is, turned off, and the charging voltage of the capacitor C1 is fixed to the value at the time of automatic light amount control. Thereby, the voltage of the inverting input terminal and the output terminal of the operational amplifier OP1 is held until the switch SWAPC1 is turned on again and the next automatic light quantity control is started.

  At the same time, the switch SWAPC2 is switched to the terminal a. The capacitor C2 is charged with the voltage output from the photodiode PD at the end of automatic light quantity control. Since the operational amplifier OP1 has a buffer function, it outputs a voltage equal to the voltage charged in the capacitor C1. As a result, the output voltage of the photodiode PD at the end of the automatic light amount control is held until the next automatic light amount control is started.

  As described above, even when the automatic light amount control is finished, this surface emitting laser driving device holds the output voltage of the operational amplifier OP1 at the end of the control, that is, the control voltage of the complementary current sources Is1 to Isn. The output voltage of the photodiode PD at the end of control can be held. As a result, the next automatic light amount control start can be controlled using these held voltages, so that the start of rising can be accelerated and the convergence time can be shortened.

  In addition, this surface emitting laser driving device can also suppress fluctuations in the output of the operational amplifier OP1 when the channel ch is switched to control the light quantity of each of the surface emitting lasers LD1 to LDn.

  FIG. 20 is a timing chart showing the result of convergence when automatic light quantity control is performed by continuously switching the switches SW1 to SWn. This timing chart shows how the output value of the operational amplifier OP1 held at the end of the previous automatic light amount control and the current convergence value are shifted to the convergence value by performing the light amount control.

  From the upper part of the timing chart, the optical output incident on the photodiode PD, the output of the operational amplifier OP1, the switches SW1, SW2... SWn for switching the channel, on / off of the surface emitting lasers LD1, LD2,. , APCCONT is turned on / off. APCCONT is turned on when automatic light quantity control is performed in any channel ch.

  In automatic light quantity control, channel ch1 control is started from time T1, and then channel switching is continuously performed until channel ch_n, and the surface emitting lasers LD1 to LDn are turned on and off to perform automatic light quantity control in synchronization therewith. I do.

  The convergence time when the channel ch is continuously switched without interruption is much shorter than the total convergence time when the automatic light amount control is performed separately for each channel ch. Further, in this case, the light beam converges to the target light output while being attenuated as if the same channel ch is continuously controlled with automatic light quantity control.

  When the automatic light quantity control is repeatedly performed in combination with the method of holding the output of the operational amplifier OP1 and the photodiode PD at the time when the automatic light quantity control described above is completed and using it as the initial value of the next automatic light quantity control, even if it is per channel Even if the convergence time is short, the target light intensity can be obtained in all channels. However, when the time lag becomes large, the monitor voltage value input to the operational amplifier OP1 deviates from the reference value Vref during a period in which the switch change occurs, and the output of the operational amplifier OP1 varies greatly. For this reason, variation occurs in the automatic light amount control convergence value for each surface emitting laser LD, and in order to converge this, it is necessary to take a long convergence time.

  Further, according to the timing chart shown in FIG. 21, even if a modulation period is provided after the light quantity control, the receiver output and the ratio stage output are held during the modulation period, and the next automatic light quantity control is performed the previous time. By starting from the final voltage in the automatic light amount control, it is possible to converge to the target light amount as if the light amount control was continuously performed without the modulation period.

  For example, at time T1f, the first automatic light amount control is completed for all channels ch, but the output of the operational amplifier OP1 has not yet converged. However, at the start of the next automatic light quantity control (time T2s), the light quantity control starts from the output at the time T1s at the end of the previous time, and therefore converges in the same manner as the continuous light quantity control. By repeating this operation, the automatic light quantity control converges at Tns, and a target light output is obtained.

  Even when automatic light quantity control is intermittently performed in this way, it can be converged as if automatic light quantity control is performed continuously for a long time with one surface emitting laser LD, and the accuracy of automatic light quantity control is improved. It is possible to improve.

  Even if one automatic light quantity control is short, if this is repeated intermittently, the light quantity converges to the target value. Therefore, if the light intensity control is continuously performed for light intensity control as in laser xerography, even if the photoconductor is exposed to light and waste of toner or deterioration of the photoconductor occurs, it is automatically performed intermittently. Since the amount of light can be controlled, unnecessary exposure to the photoreceptor can be prevented. This is particularly effective in the case of xerography where toner cleaning is omitted. In the case of a multi-laser, although the time for automatic light amount control per channel is short, the light amount control for each scan can be performed. Therefore, if the laser characteristic variation is small for each scan, it is possible to sufficiently correct the characteristic variation by controlling the amount of light for each scan.

2. Configuration of Multilaser Hereinafter, a constant voltage driving type using a common power source, a constant voltage driving type using a diode, and a constant current driving type will be described.

(1) Constant Voltage Drive Type Using a Common Power Supply The constant voltage drive type surface emitting laser drive device is composed of 36 channels as shown in FIG. 22, and is common to the termination resistors R_1 to R_36 of each channel ch. A voltage source B5 as a power source is provided, and a current flowing into the voltage source B5 is made constant regardless of whether the surface emitting lasers LD_1 to LD_36 are turned on or off.

  The surface emitting laser driving device includes a light emitting unit 10 composed of a surface emitting laser LD, a current supply unit 20 composed of current sources Is, Is ′, Ic, etc., a setting unit 30 composed of comparators A2, A3, etc. The power source unit 40 includes voltage sources B5 and B6, and the light receiving unit 50 includes photodiodes PD, amplifiers A5 and A6, and the like. The light emitting unit 10 and the current supply unit 20 are provided for each channel ch.

(Configuration of the light emitting unit 10 and the current supply unit 20)
Each channel ch is configured identically. Here, channel ch1 will be described as an example.

  The channel ch1 includes complementary current sources Is, Is ′ to which a predetermined voltage is applied on the input side, current sources Ic to which the output side is grounded, switches SWsh, SWs, SWc, and control voltages for the complementary current sources Is. And a capacitor Csw for holding the signal.

  The output side of the complementary current source Is is connected to the switch SWs. The switch SWs outputs the complementary current Is from the complementary current source Is via the terminal a or the terminal b. The switch SWs is the same as that shown in FIG. 23, and is composed of a current switch having a PMOS differential configuration, for example. The terminal a of the switch SWs is connected to the anode of the surface emitting laser LD_1, and further connected to the output terminal of the voltage source B5 via the termination resistor R_1. The terminal b of the switch SWs is connected to the termination resistor R4, and is also connected to the output terminal of the voltage source B5.

  The switch SWc supplies the current from the terminal a or the terminal b to the current source Ic. The output side of the current source Ic is grounded. Here, the terminal a of the switch SWc is connected to the terminal a of the switch SWc provided in the other channel ch, and is also connected to the output side of the voltage source B6. The terminal b of the switch SWc is connected to the terminal b of the switch SWs.

  The current source Is ′ is a current mirror circuit, and supplies a current Is ′ proportional to the complementary current Is output from the complementary current source Is to the common resistor VR1. The terminal voltage of the common resistor VR1 becomes the control voltage of the current source Ic.

  In such a configuration, when the surface emitting laser LD_1 is off, the switch SWs and the switch SWc each select the terminal b. When the switch SWs and the switch SWc are respectively switched to the terminal a, the complementary current Is is supplied to the termination resistor R_1 via the switch SWs, and a part of the current flows to the laser LD_1. At this time, the current Is ′ is summed with the current Is ′ of the other channels and supplied to the resistor VR1. As a result, a voltage drop of the common resistor VR1 occurs. The current source Ic is controlled by the voltage generated by the common resistor VR1 when the voltage drops. The current source Is' is not connected to the switch, and the control voltage of the current source Ic is continuously applied.

  Here, the current Ic is made to correspond to the current flowing through the laser LD_1 by adjusting the common resistance VR1 to an appropriate value. Thereby, the current Ic output from the current source Ic can be set to a constant ratio of the complementary current Is.

  When the surface emitting laser LD_1 is turned off, the switch SWs and the switch SWc each select the terminal b. The complementary current Is output from the complementary current source Is is supplied to the common voltage source B5 through the switch SWs by subtracting the current Ic. As described above, the current Ic is a current corresponding to a constant ratio of Is. Therefore, the current (Is-Ic) after subtraction coincides with the current flowing through the termination resistor R_1 when the surface emitting laser LD_1 is on, and is supplied to the voltage source B5. Therefore, the current supplied to the voltage source B5 can be made equal regardless of whether the surface emitting laser LD_1 is on or off. That is, the output impedance of the voltage source B5 can be made constant.

(Configuration of setting unit 30)
Next, the comparator A2 and the comparator A3 that are commonly used in each channel ch will be described.

  The comparator A3 sets the output potential of the voltage sources B5 and B6. The capacitor C3 is for holding the control voltage during modulation and starting the next APC from the final voltage of the previous APC. Therefore, one end of the capacitor C3 is connected to the output side of the comparator A3, and the other end is connected to the inverting input terminal of the comparator A3.

  One end of the resistor R4 is connected to the terminal a of the switch SW4 and further connected to the input side of the current source I1. The other end of the resistor R4 is connected to the terminal b of the switch SW4 and further connected to the positive electrode of the constant voltage source Vref. The switch SW4 supplies the voltage at the terminal a or the terminal b to the non-inverting input terminal of the comparator A3.

  For example, when the switch SW4 selects the terminal a, the voltage Vref of the constant voltage source Vref is applied to the non-inverting input terminal of the comparator A3 via the resistor R4. This voltage Vref is a target value for automatic light quantity control. When the switch SW4 selects the terminal b, a low voltage (= Vref−current I1 × resistance R4) is applied to the non-inverting input terminal of the comparator A3.

  The comparator A3 sets the output voltage of the voltage sources B5 and B6. The non-inverting input terminal of the comparator A3 is connected to the switch SW4 as described above. The inverting input terminal of the comparator A3 is connected to the output terminal of the amplifier A5 via the switch SW2, and further connected to the output terminal of the comparator A3 via the capacitor C3. Here, the output voltages of the voltage sources B5 and B6 are set to be the oscillation threshold value of the surface emitting laser LD_1. If the output voltages of the voltage sources B5 and B6 are slightly lower than the oscillation threshold, it is possible to prevent the laser from emitting light during the off period. How much lower depends on the current source I1. However, if it is too small, light emission cannot be stopped, and if it is too large, power consumption cannot be reduced by the voltage source B5 connected in series to the termination resistor R_1.

  The comparator A2 sets the control voltage of the complementary current source Is of each channel ch. The non-inverting input terminal of the comparator A2 is connected to the constant voltage source Vref. The inverting input terminal of the comparator A2 is connected to the output terminal of the amplifier A5 via the switch SW2. Similarly to the comparator A3, the comparator A2 is connected to a capacitor C2 that serves both for phase compensation and holding and to a switch SW2 for holding. Specifically, one end of the capacitor C2 is connected to the output terminal of the comparator A2, and the other end is connected to the inverting input terminal of the comparator A2.

  The limiter voltage is further input to the comparators A2 and A3. Comparators A2 and A3, which are operational amplifiers with limiters, are composed of, for example, a CMOS as shown in FIG.

  Here, the surface emitting laser LD_1 has a region in which the amount of light decreases even when the current is increased. Therefore, in order to set a voltage smaller than the voltage at which the light amount of the surface emitting laser LD_1 starts to decrease, the limiter voltage Vlimit2 is set in the comparator A3. Similarly to the above, there is a region where the light amount of the surface emitting laser LD_1 decreases even when the complementary current Is increases. Therefore, the limiter voltage Vlimit1 is set in the comparator A2 so as to set the control voltage of the complementary current source Is so as not to enter this region. The voltage Vref of the constant voltage source Vref is the light receiver output voltage when the target light quantity is obtained.

(Configuration of power supply unit 30)
The voltage source B5 is a voltage source common to each channel ch. The output terminal of the voltage source B5 is connected to the anode of the surface emitting laser LD_1 through the termination resistor R_1. Similarly, in the other channel ch, the output terminal of the voltage source B5 is connected to the anodes of the surface emitting lasers LD_2 to LD_36 via the terminating resistors R_2 to R_36. The cathodes of the surface emitting lasers LD_1 to LD_36 are grounded.

  The voltage source B6 supplies a control voltage to the current source Ic to fix the correction current Ic of each channel ch when the surface emitting laser LD_1 is turned on (when the switch SWc selects the terminal a). This prevents the switching speed of the switch SWc from decreasing.

(Configuration of the light receiving unit 50)
The surface emitting lasers LD_1 to LD_36 are optically coupled to a photodiode PD which is one light receiver. A predetermined voltage is applied to the cathode side of the photodiode PD. The anode side of the photodiode PD is connected to the resistor R5 or the resistor R6 via the switch SW5. The other ends of the resistors R5 and R6 are grounded. The resistor R5 and the resistor 6 have the following relationship.

(Resistance value of resistor R6) = (resistance value of resistor R5) × (number of beams (= 36))
When the amount of light per beam is equal, according to the above formula, the terminal voltage when one beam is turned on and the resistor R6 is connected, and the terminal voltage when all the beams are turned on and the resistor R5 is connected. Are equal to each other. As a result, when all the beams are turned on and output with a low resistance R5, the time constant of the light receiver can be reduced to 1 / number of beams, and the convergence time of APC can be shortened. This is particularly effective when time is required for convergence, such as when power is turned on.

  The switch SW6 supplies the terminal voltage of the resistor R5 or the resistor R6 to the non-inverting input terminal of the amplifier A5, and further supplies the terminal voltage to the switch SW7. The inverting input terminal of the amplifier A5 is grounded via the resistor R7, and further connected to the output terminal of the amplifier A5 via the resistor R8. Therefore, the amplifier A5 amplifies the voltage input to the non-inverting input terminal and outputs it via the output terminal.

  The switch SW7 selects the terminal a or the terminal b. The terminal a of the switch SW7 is connected to the non-inverting input terminal of the amplifier A6, and is further grounded via the capacitor C6. The terminal b of the switch SW7 is connected to the inverting input terminal and the output terminal of the amplifier A6.

  The amplifier A6, the capacitor C6, and the switch SW7 have a function of holding the terminal voltage of the resistor R5 or the resistor R6. During the automatic light amount control, the switch SW7 selects the terminal a and connects it to the capacitor C6 side. Then, the terminal voltage of the resistor R5 or the resistor R6 is supplied to the capacitor C6. When the automatic light quantity control ends, the switch SW7 selects the terminal b and connects it to the output terminal of the amplifier A6. Then, the final voltage of APC, that is, the voltage of the capacitor C6 is output from the output terminal of the amplifier A6 and supplied to the non-inverting input terminal of the amplifier A5. That is, the terminal voltage of the resistor R5 or the resistor R6 is held.

(Overall operation)
These operations will be described with reference to time charts of FIGS. 25 and 26. Note that each double-throw switch SW shown in FIG. 22 is in a laser-off state, and the laser is turned on when each double-throw switch is switched. This is the same in the following description.

  After the power is turned on, the output of the comparator A3 is first set to adjust the output potential of the voltage sources B5 and B6. Specifically, the switch SW3 is turned on, the SW4 is switched to the terminal b, and the full surface emission lasers LD_1 to LD_36 are turned on. Then, automatic light quantity control is performed so that the output of the amplifier A5 becomes equal to the reference voltage Vref. At this time, the switch SWc and the switch SWs both select the terminal b as shown in FIG.

  Each of the surface emitting lasers LD_1 to LD_36 is turned on when a current is supplied through each of the terminating resistors R_1 to R_36. Then, automatic light quantity control is performed to set the output potential of the voltage sources B5 and B6.

  Here, the power per beam is a fraction of the number of beams of the voltage Vref. Therefore, if the number of beams is large, the voltage sources B5 and B6 are set to a value substantially equal to the laser oscillation threshold voltage. However, in this state, the photosensitive member is exposed and fogging occurs. Therefore, the switch SW4 is further switched to the terminal a to hold the voltage of the capacitor C3. As a result, the potential at the non-inverting input terminal of the comparator A3 is lowered by the voltage drop that causes the current I1 to flow through the resistor R4 to obtain the final voltage of the voltage sources B5 and B6.

  That is, at the end of the light amount control, the switch SW3 is turned off at time T1- shown in FIG. 22, and the voltage between the output terminal and the inverting input terminal of the comparator A3 is held. Further, the switch SW7 is switched to the terminal b to hold the output.

  Thereafter, at time T1, the switch SW4 is switched to the terminal b. The output of the comparator A3, that is, the output voltage of the voltage sources B5 and B6 is set slightly lower than that at the end of the automatic light amount control as described above. Thereby, the surface emitting laser LD_1 does not emit light, and power consumption can be reduced.

(Average value setting of complementary current Is)
Next, in order to set the average value of the complementary currents Is flowing through the surface emitting lasers LD_1 to LD_36, automatic light quantity control is performed when the entire surface emitting lasers LD_1 to LD_36 are turned on.

  At time T1 +, the switches SW5 and SW6 are switched to the resistor R5 side. This shortens the time constant and shortens the convergence time. Further, the switch SW2 is turned on, the switch SW7 is switched to the terminal a side, and negative feedback control is performed using the comparator A2.

  At the same time, at time T1 +, the switches SWs and SWc of all channel channels are switched to the terminal a, the surface emitting lasers LD_1 to LD_36 are turned on, and the switches SWch of all channel channels are turned on so that the capacitor Csw can be charged. Automatic light quantity control.

  After the automatic light amount control has converged, at time T2-, the switches SWch of all channel channels are turned off simultaneously, and the control voltage of the complementary current source Is of each channel channel is sampled and held to set the average value of the complementary currents Is.

  Further, the switch SW2 is turned off, and the switch SW7 is switched to the terminal b. Thereby, the output of the comparator A2 and the output of the amplifier A6 are held until the next light amount control. Further, the switches SWs of the channels ch2 to ch36 are switched to the terminal b, and the surface emitting lasers LD_2 to LD_36 other than the channel ch1 are turned off.

  In the first automatic light amount control immediately after the power is turned on, the light receiver output and the comparator output greatly deviate from the convergence value, and the convergence time becomes longer. In this case, the convergence time is shortened by selecting the resistor R5 so that the convergence time constant is shortened as described above, turning on the entire surface emitting lasers LD_1 to LD_36, and setting the average of the complementary currents Is. Can do.

  Next, the operation after the completion of setting the average value of the complementary current Is will be described.

  Each of the surface emitting lasers LD_1 to LD_36 emits light with a target amount of light, but there is still considerable variation in the amount of emitted light due to variations in characteristics. Therefore, automatic light amount control is performed for each channel individually to bring it closer to the target light amount. Further, compared with the normal operation period (T9 + to T17) in which the modulation operation and the automatic light amount control are repeated, the variation in the light emission amount is still large at this stage and it takes time to converge. Therefore, it is necessary to set a longer time for the automatic light amount control for each channel. In addition, since it can be converged to the final value even by the intermittent automatic light amount control, the light amount control timing at the time of image writing may be used when it is not desired to expose the photosensitive member.

  Specifically, at time T2, both the switch SW5 and the switch SW6 are switched to the resistor R6 side, and at the same time, both the switch SWs and the switch SWc of the channel ch1 are switched to the terminal a. Thereby, the surface emitting laser LD_1 is turned on continuously from the time of setting the average value of the complementary currents Is.

  Thereafter, at T2 +, the switch SW2 and the switch SWch are turned on, the switch SW7 is switched to the terminal a, and the automatic light quantity control of the channel ch1 is started.

  Here, the timing for switching the channel ch will be described by taking as an example the case of switching from the channel ch1 to the channel ch2.

  After the automatic light quantity control of the channel ch1 is completed, at time T3-, the switch SWsh is first turned off, and the control voltage of the complementary current source Is is sampled and held. Further, the switch SW2 is turned off at the same timing, the switch SW7 is switched to the terminal b, and the output of the amplifier A5 and the output of the comparator A2 are held.

  At time T3, the switches SWs and SWc of the channel ch1 are switched to the terminal b, and the switches SWs and SWc of the channel ch2 are switched to the terminal a. Thereby, the surface emitting laser LD_1 of the channel ch1 is turned off, and the surface emitting laser LD_2 of the channel ch2 is turned on.

  Such turn-off and turn-on are preferably switched continuously without a time interval or overlapping. However, if the switching is continuously performed on the order of several tens of nsec, a large error does not occur in the amount of convergent light of each of the full surface emission lasers LD_1 to LD_36.

  At time T3 +, the switch SWch of channel ch2 is turned on, and automatic light quantity control of channel ch2 is started. As described above, when the SWch is turned on in a certain channel chN and automatic light quantity control is performed, the timing is set so that the Nth surface emitting laser LD_N is always turned on.

  If the switching operation between turning off and lighting can be performed ideally continuously, the output of the comparator A2 and the amplifier A5 while the switch SW2 is turned on and the switch SW7 is set to the terminal a during the switching period between the channel channels. It is also possible to continue the automatic light quantity control of each channel sequentially without holding the.

  Hereinafter, although omitted in the timing chart, channel switching is performed at the same timing from channel ch1 to channel ch36, and automatic light quantity control is sequentially performed from the surface emitting laser LD_1 to the surface emitting laser LD_36.

  At the timing so far (time T5-), the output setting of the comparator A3, the average value of the complementary current Is, and the output setting of the channels ch1 to ch36 have been performed. Further, before the shift to the modulation operation, automatic light quantity control is performed in the period T5 + to T6- in order to set the output of the comparator A3 again and the output for each of the channels ch1 to ch36 in the period T6 + to T9. By repeating in this way, the accuracy of the convergence value of automatic light quantity control can be improved.

  However, since the convergence value close to the target setting value has already been obtained, the convergence value can be obtained in a shorter time in the second automatic light amount control than in the first time. After the second automatic light amount control is completed, the modulation operation is started from time T9 +. Thereafter, after T10, the automatic light amount control and the modulation operation for each channel are repeated, and the light amount is held at the target value and the circuit driving operation is performed.

(2) Constant Voltage Drive Type Using Diode Next, a voltage drive type surface emitting laser drive device using a diode will be described. Note that the description overlapping with the surface emitting laser driving device shown in FIG. 22 is omitted.

  As shown in FIG. 27, the surface emitting laser driving apparatus reduces power consumption by connecting two silicon diodes D1 and D2 to termination resistors R_1 to R_36. Although this surface emitting laser driving device has a large number of parts, since the output circuit is independent, there is an advantage that crosstalk due to voltage fluctuation of the common voltage source does not occur.

  In this surface emitting laser driving apparatus, as compared with the apparatus shown in FIG. 22, the voltage source B5 is replaced with a series circuit of silicon diodes D1 and D2, and the current source Ic is replaced with a bias current source Ib.

(Device configuration)
Each channel ch is configured the same, and here, channel ch1 will be described as an example.

  The channel ch1 includes a bias current source Ib and a complementary current source Is to which a predetermined voltage is applied on the input side, a switch SWs that outputs the complementary current Is output from the complementary current source Is from the terminal a or the terminal b, and a bias A switch SWb for turning on / off the control voltage supplied to the current source Ib and a switch SWsh for turning on / off the control voltage supplied to the complementary current source Is are provided.

  One end of the termination resistor R_1 is connected to the anode side of the surface emitting laser LD_1. The other end of the termination resistor R_1 is connected to the anode side of the silicon diodes D1_1 and D2_1 connected in series. The surface emitting laser LD_1 and the cathode side of the silicon diode D2 are grounded.

  The bias current source Ib supplies the bias current source Ib from the anode side of the surface emitting laser LD_1. When the switch SWs is switched to the terminal a, the switch SWs supplies the complementary current Is to the surface emitting laser LD_1 and the termination resistor R_1. When the switch SWs is switched to the terminal b, the switch SWs supplies the complementary current Is to the silicon diodes D3_1, D4_1, and D5_1 connected in series.

  The setting unit 30 and the light receiving unit 50 are configured similarly to the surface emitting laser driving apparatus shown in FIG. The comparator A2 supplies a control voltage to the complementary current source Is through the switch SWsh. The comparator A3 supplies a control voltage to the bias current source Ib via the switch SWb so that the bias current Ib is close to the oscillation threshold value of the surface emitting laser LD.

(Overall operation)
In the surface emitting laser driving apparatus configured as described above, the switch SW4 is switched to the terminal b in the same manner as in FIG. Then, a voltage reduced by the potential determined by the switch SW4 is input to the non-inverting input terminal of the comparator A3 so that the surface emitting laser LD_1 does not emit light during the off period. The potential finally becomes the control voltage of the bias current source Ib of each channel ch.

  Next, the operation will be described with reference to time charts of FIGS. The difference from the timing charts of FIGS. 25 and 26 described above is that the bias current source Ib shown in FIG. 27 is set instead of the output setting of the voltage source B5 shown in FIG. As shown in FIGS. 28 and 29, the bias current source Ib is set in the periods T0 to T1 and T5 + to T6-.

  First, at time T0 after power-on, switch SW3 is turned on, SW4 is switched to terminal b, and at the same time, switch SWb for each channel ch is turned on. The comparator A3 sets the control voltage of the bias current source Ib.

  At times T1 and T1-, these switches SW are turned off, and the setting of the control voltage of the bias current source Ib is completed. Similarly, the control voltage of the bias current source Ib is set in the period T5 + to T6-. The switch SWb of each channel ch is in an off state except for this timing. Then, instead of setting the output potential of the voltage source B5 shown in FIG. 22, the timing is the same as the timing of FIGS. 25 and 26 described above except that the control voltage of the bias current source Ib is set.

(3) Constant Current Drive Type Next, a constant current drive type surface emitting laser drive device will be described. This surface-emitting laser driving device has a feature that wasteful current does not flow because there is no terminal resistance. However, since the single mode surface emitting laser has a very large internal resistance, the modulation speed cannot be increased by constant current driving. Therefore, as shown in FIG. 30, the surface emitting laser driving apparatus superimposes a capacitor Csb, a switch SWsu driven in synchronization with the on / off of the surface emitting laser LD, and a differential current (pulse signal Vpulse). A differential current superposition circuit using a capacitor Csu or the like is provided.

(Device configuration)
Specifically, the surface emitting laser driving device includes a light emitting unit 10, a current supply unit 20, a setting unit 30, and a light receiving unit 50. Note that a part of the setting unit 30 and the light receiving unit 50 are configured in the same manner as in FIGS. 22 and 27, and only different parts will be described.

  The current supply unit 20 includes a bias current source Ib and a complementary current source Is to which a predetermined voltage is applied on the input side, switches SWb, SWsh, SWs, SWsu, and capacitors Cbi, Csw, Csb, Csu. Yes.

  The bias current source Ib supplies the bias current Ib to the anode side of the surface emitting laser LD_1. The cathode side of the surface emitting laser LD_1 is grounded. The control voltage of the bias current source Ib is supplied from the comparator A3. The capacitor Cbi holds this control voltage.

  The complementary current source Is supplies the complementary current Is to the switch SWs according to the control voltage set by the comparator A2. The switch SWs outputs the complementary current Is from the complementary current source Is from the terminal a or the terminal b. The terminal a of the switch SWs is connected to the anode side of the surface emitting laser LD_1, and is further connected to the switch SWsu via the capacitor Csu. The terminal b of the switch SWs is connected to two capacitors Cx and Cy connected in parallel, and is further connected to the terminal b of the switch SWs of another channel ch. The other ends of the capacitors Cx and Cy are grounded.

  The terminal a of the switch SWsu is connected to one end of the capacitor Csb and further connected to the output terminal of the comparator A1. The terminal b of the switch SWsu is grounded and connected to the other end of the capacitor Csb.

  The setting unit 30 includes comparators A1, A2, and A3. The non-inverting input terminal of the comparator A1 is connected to the constant voltage source Vref. The inverting input terminal of the comparator A1 is connected to the output terminal of the amplifier A5 via the switch SW1, and further connected to the output terminal of the comparator A1 via the capacitor C1. The comparator A1 outputs a predetermined voltage to the switch SWsu so that the output voltage from the amplifier A5 matches the reference voltage Vref.

  The comparator A2 supplies a control voltage to the complementary current source Is via the switch SWsh for each channel ch. The comparator A3 supplies a control voltage to the bias current source Ib via the switch SWb for each channel ch.

  The switches SWsu and SWs are preferably configured using a CMOS process, as shown in FIG. Thereby, it can prevent that a phase shifts at the time of a differential current superposition. Here, since the voltage Vcc is used as a reference, the control may be difficult. Therefore, as shown in FIG. 31, the voltage Vss can be used as a reference using NMOS. In this case, a delay corresponding to one gate stage occurs with respect to the switch SWs, but there is no particular problem if the delay per gate stage is set to 1 nsec or less unless modulation is performed with a pulse width of several nsec. The amplitude of the differential current is controlled by the comparator A1, which adjusts the phase compensation by making the light quantity when APC is performed with continuous lighting equal to the light quantity when pulse lighting is performed. The

(Overall operation)
The surface emitting laser driving apparatus configured as described above will be described with reference to timing charts shown in FIGS.

  The control setting of the differential current superimposing circuit is repeated in the timing chart shown in FIG. 32 by using the comparator A1 and repeating the sequence of lighting the surface emitting laser LD in order from the channel ch1 to the channel ch36. The comparator A1 controls the amplitude (level of the pulse signal Vpulse) of the differential current superposition circuit so that the output of the amplifier A5 at this time matches Vref. Here, the control is not performed for each channel ch by changing the bias current Ib, but all channels ch are controlled at once. For this reason, it is necessary to prevent the parasitic capacitance up to the surface emitting laser LD from varying between the channels ch in advance.

  The operation of this surface emitting laser driving apparatus is the same as that performed for the surface emitting laser driving apparatus shown in FIG. That is, in the case of overcompensation, overshoot occurs and the light quantity exceeds Vref. If the compensation is insufficient, it falls below the reference voltage Vref, but the compensation is optimal when the output of the amplifier A5 matches the reference voltage Vref. At this time, there is no overshoot or undershoot.

  This control is performed before modulation after the automatic light amount control of each channel from the period T5 to T6 is completed. Here, the control voltage of the differential current superposition circuit is held by the capacitor Csb. However, since the differential current amplitude does not change significantly, it may be digitally performed using a D / A converter. The calibration in this case is, for example, between pages or after power-on, but there is no practical problem.

3. Other Configurations FIG. 34 is a diagram for explaining that the setting unevenness at the time of automatic light quantity control is made inconspicuous by randomizing the order of automatic light quantity control.

  When automatic light quantity control is continuously performed on all channels, the final voltage of the previous channel ch affects the start voltage of the next channel ch. If the final voltage variation between channels ch is large due to variations in the characteristics of the surface emitting laser LD, the output of the comparator cannot be sufficiently converged, and light intensity control as shown in FIGS. 34 (a) to (d) is performed. Specific noise may occur in turn. As shown in FIG. 5E, if the light quantity control order is made to correspond to the position order of the surface emitting laser LD at this time, variations in the low frequency component occur in the light quantity distribution of the laser, causing image quality deterioration. Become. Therefore, if the order of light quantity control is made to have no correlation with the arrangement of the lasers as shown in FIG. 5F, the light quantity distribution of the lasers is shifted to frequency components with high variations, and image quality deterioration can be prevented.

  The surface emitting laser driving device described above has been described on the assumption that there is no significant difference in the control voltage in each channel ch. However, there may be a difference in the control voltage between channels due to the threshold current and emission efficiency of the surface emitting laser or the offset of the operational amplifier used in the constant current circuit in the channel. If this difference does not converge within the automatic light quantity time of one channel, the variation between the entire channels ch deteriorates and the image quality deteriorates.

  In such a case, as shown in FIG. 35, a surface emitting laser driving device with offset cancellation is preferable. This surface emitting laser driving apparatus corresponds to one channel of the surface emitting laser driving apparatus shown in FIG. A waveform diagram when each switch SW is turned on / off is shown in FIG. Note that the switches SWoa and SWob shown in FIG. 35 are on.

  In this surface emitting laser driving device, the capacitors Co1 and Co2 are charged by the terminal voltage of the capacitor Cs common between the channels ch and the control voltage for each channel ch output from the comparator A2. The amplifier As cancels variations including the offset of the operational amplifier As itself by comparing the voltage from the comparator A2 supplied to the non-inverting input terminal with the voltages of the capacitors Co1 and Co2.

  When the power is turned on or between pages, the offset storage capacitor Co1 is short-circuited by the switch SWod, and in this state, the automatic light amount control of each channel ch is performed over a period of time. After that, if the control signal output to each channel ch at the time of automatic light amount control for each scan is stored in Co2, and the terminal voltage of Co1 is corrected, the offset can be canceled by several corrections.

  Moreover, you may comprise the surface emitting laser drive device as shown in FIG. This surface emitting laser driving apparatus is different from that shown in FIG. 30 in that a plurality of capacitors C are provided between the inverting input terminal and the output terminal of the comparator A2. Specifically, 36 capacitors C2_1, C2_2,..., C2_36 connected in parallel are provided between the inverting input terminal and the output terminal of the comparator A2. The switches SW1, SW2,..., SW36 are provided at one end of each of the capacitors C2_1, C2_2,. For example, the switch SW1 is turned on when the light amount control of the channel ch1 is performed, and the switch SW2 is turned on when the light amount control of the channel ch2 is performed.

  As a result, the capacitor C1_1 is charged by the control voltage of the comparator A2 when the light amount of the channel ch1 is controlled. The comparator A2 can set the control voltage of the bias current source Ib using the voltage of the capacitor C1_1 when the light amount control of the channel ch1 is performed next time.

  Therefore, even if the output voltage of the comparator A2 varies for each channel ch, the surface emitting laser driving apparatus does not use the output voltage for the light amount control of the other channel ch, but for the light amount control of the same channel ch. ing. Thereby, even if the control voltage of the comparator A2 varies for each channel ch, it is possible to prevent the convergence time of the automatic light amount control from becoming long.

It is a circuit diagram which shows the structure of the basic voltage drive type surface-emitting laser drive device of this invention. It is a figure which shows the characteristic of the electric current with respect to the terminal voltage of a surface emitting laser. It is a circuit diagram which shows the structure of the basic voltage drive type surface-emitting laser drive device of this invention. It is a circuit diagram which shows the structure of the rough current drive type surface emitting laser drive device of this invention. It is a figure which shows the voltage when the voltage converged and the overshoot. It is a figure which shows the characteristic of the electric current which flows through a surface emitting laser with respect to the voltage applied to a surface emitting laser. It is a figure explaining compensating for distortion of a waveform with Vpulse and bias current Ib. It is a circuit diagram which shows the structure of the basic current drive type surface emitting laser drive device of this invention. It is a figure explaining the case of overcompensation and the case of insufficient compensation. It is a circuit diagram which shows the structure of the other other current drive type surface emitting laser drive device of this invention. It is a circuit diagram which shows the structure of the other other current drive type surface emitting laser drive device of this invention. It is a figure which shows the relationship between the average value of a laser beam, and the reference voltage V_APCREF in the case of overcompensation and the case of insufficient compensation. It is a circuit diagram which shows the structure of the other other current drive type surface emitting laser drive device of this invention. It is a circuit diagram which shows the structure of the other other current drive type surface emitting laser drive device of this invention. It is a figure which shows the relationship between the average value of a laser beam, and (reference voltage V_APCREF / 2) in the case of overcompensation and the case of insufficient compensation. It is a circuit diagram which shows the structure of the other other current drive type surface emitting laser drive device of this invention. It is a circuit diagram which shows the structure of the other other current drive type surface emitting laser drive device of this invention. It is a wave form diagram which shows a drive current when a compensation amount is controlled by a current source Is, a laser voltage, a compensation current and a drive voltage after compensation. It is a circuit diagram which shows the structure of the surface emitting laser drive device for controlling the light quantity of a surface emitting laser. It is a wave form diagram which shows the convergence of APC when the channel ch of each surface emitting laser is switched continuously. It is a wave form diagram which shows the convergence property when the channel ch of each surface emitting laser is switched and APC control is performed intermittently. It is a circuit diagram which shows the structure of the constant voltage drive type surface emitting laser drive device which concerns on embodiment of this invention. It is a circuit diagram which shows the structure of switch SWs with which the constant voltage drive type surface emitting laser drive device was equipped. It is a circuit diagram which shows the structure of the comparator with a limiter. It is a timing chart explaining the operation | movement content of a constant voltage drive type surface emitting laser drive device. It is a timing chart explaining the operation | movement content of a constant voltage drive type surface emitting laser drive device. It is a circuit diagram which shows the structure of the constant voltage drive type surface emitting laser drive device when a diode is used. It is a timing chart explaining the operation | movement content of the constant voltage drive type surface emitting laser drive device when a diode is used. It is a timing chart explaining the operation | movement content of the constant voltage drive type surface emitting laser drive device when a diode is used. It is a circuit diagram which shows the structure of the constant current drive type surface emitting laser drive device which concerns on embodiment of this invention. It is a circuit diagram which shows the structure of switch SWs with which the constant current drive type surface emitting laser drive device was equipped. It is a timing chart explaining the operation | movement content of a constant current drive type surface emitting laser drive device. It is a timing chart explaining the operation | movement content of a constant current drive type surface emitting laser drive device. It is a figure for demonstrating changing the order of APC so that the light quantity distribution frequency component of a surface emitting laser may be shifted to a high frequency side. It is a circuit diagram which shows the structure of the surface emitting laser drive device with an offset cancellation. It is a wave form diagram of each circuit of the surface emitting laser drive device with an offset cancellation. FIG. 3 is a circuit diagram showing a configuration of a current-driven surface emitting laser driving device provided with a capacitor C for each channel ch. It is a figure which shows the VI characteristic of an end surface emitting laser and a surface emitting laser. It is a circuit diagram which shows the simple structure of a current drive type surface emitting laser drive device. It is a figure explaining the problem of a current drive type surface emitting laser drive device. It is a figure which shows the VI characteristic of a surface emitting laser. It is a figure which shows the waveform at the time of VCSEL drive.

Explanation of symbols

LD Surface emitting laser Is Complementary current source Ib Bias current source R_1 to R_36 Termination resistors A1, A2, A3 Comparator PD Photodiode

Claims (16)

A surface emitting laser that outputs laser light;
A current source for supplying a current to the surface emitting laser when on the surface-emitting laser,
It controls the voltage level of the pulse voltage to be supplied to the surface emitting laser, and a pulsed voltage supply means for supplying to the surface emitting laser in synchronism with the pulse voltage the control to turn on the surface-emitting laser,
The pulse voltage supply means acquires and holds a convergence terminal voltage when the surface emitting laser is turned on and the terminal voltage of the surface emitting laser is substantially converged, and when the surface emitting laser is turned on and starts up The surface emitting laser driving apparatus according to claim 1, wherein the voltage level is controlled so that a terminal voltage of the surface emitting laser coincides with the held convergence terminal voltage . The pulse voltage supply means includes
A first capacitor for acquiring and holding the convergence terminal voltage;
An operational amplifier that controls the voltage level based on the convergence terminal voltage held by the first capacitor;
A second capacitor holding a voltage level controlled by the operational amplifier;
The surface emitting laser driving device according to claim 1, comprising: The pulse voltage supply means is a capacitor connected in series with the second capacitor in synchronization with the surface emitting laser being turned on, and supplies a pulse voltage to the surface emitting laser together with the second capacitor. 3. The surface emitting laser driving device according to claim 2, further comprising three capacitors. 4. The surface emitting laser driving device according to claim 1, further comprising bias current supply means for supplying a bias current to the surface emitting laser. A surface emitting laser that outputs laser light;
A current source for supplying a current to the surface emitting laser when the surface emitting laser is turned on;
A pulse voltage supply means for controlling a voltage level of a pulse voltage supplied to the surface emitting laser, and supplying the controlled pulse voltage to the surface emitting laser in synchronization with turning on of the surface emitting laser;
A light receiving means for receiving the laser light of the surface emitting laser and outputting a light receiving signal corresponding to the received laser light amount;
With
The pulse voltage supply means acquires the light reception signal, and when the one laser is continuously turned on, the acquired light reception signal is matched with a reference voltage corresponding to the light reception signal output from the light reception means. The surface emitting laser driving device characterized in that the voltage level is controlled based on the above. The pulse voltage supply means includes
An operational amplifier that controls the voltage level based on the acquired light reception signal and a reference voltage corresponding to the light reception signal output from the light receiving means when one laser is continuously turned on,
A first capacitor holding a voltage level controlled by the operational amplifier;
The surface emitting laser driving device according to claim 5, comprising: The pulse voltage supply means is a capacitor connected in series with the first capacitor in synchronization with the surface emitting laser being turned on, and supplies a pulse voltage to the surface emitting laser together with the first capacitor. The surface emitting laser driving device according to claim 6, further comprising two capacitors. 8. The surface emitting laser driving device according to claim 5, further comprising bias current supply means for supplying a bias current to the surface emitting laser. A surface emitting laser that outputs laser light;
Bias current supply means for supplying a bias current to the surface emitting laser;
A current source for supplying a current to the surface emitting laser when the surface emitting laser is turned on;
Pulse voltage supply means for supplying a fixed pulse voltage to the surface emitting laser in synchronization with the surface emitting laser being turned on,
Bias current control means for controlling the current value of the bias current,
The bias current control means acquires and holds a convergence terminal voltage when the surface emitting laser is turned on and the terminal voltage of the surface emitting laser is substantially converged, and when the surface emitting laser is turned on and starts up A surface emitting laser driving apparatus, wherein the current value of the bias current is controlled so that a terminal voltage of the surface emitting laser is equal to the held convergence terminal voltage . The bias current control means includes
A first capacitor for acquiring and holding the convergence terminal voltage;
A first operational amplifier that controls the current value based on the convergence terminal voltage held by the first capacitor;
10. The surface emitting laser driving device according to claim 9, further comprising: The pulse voltage supply means includes
A second operational amplifier that outputs a fixed voltage corresponding to the reference voltage;
A second capacitor for holding a voltage level output by the second operational amplifier;
The surface emitting laser driving device according to claim 9, wherein the surface emitting laser driving device is provided. The pulse voltage supply means is a capacitor connected in series with the second capacitor in synchronization with the surface emitting laser being turned on, and supplies a pulse voltage to the surface emitting laser together with the second capacitor. The surface emitting laser driving device according to claim 11, further comprising three capacitors. A surface emitting laser that outputs laser light;
Bias current supply means for supplying a bias current to the surface emitting laser;
A current source for supplying a current to the surface emitting laser when the surface emitting laser is turned on;
Pulse voltage supply means for supplying a fixed pulse voltage to the surface emitting laser in synchronization with the surface emitting laser being turned on,
Bias current control means for controlling the current value of the bias current;
A light receiving means for receiving the laser light of the surface emitting laser and outputting a light receiving signal corresponding to the received laser light amount;
With
The bias current control means obtains the light reception signal so that it matches the first reference voltage corresponding to the light reception signal output from the light reception means when one laser is continuously turned on. A surface emitting laser driving device that controls a current value of the bias current based on the received light signal. The bias current control unit controls the current value based on the acquired light reception signal and a first reference voltage corresponding to the light reception signal output from the light reception unit when one laser is continuously turned on. 14. The surface emitting laser driving device according to claim 13, further comprising a first operational amplifier . The pulse voltage supply means includes
A second operational amplifier that outputs a fixed voltage corresponding to the second reference voltage;
A first capacitor for holding a voltage level output by the second operational amplifier;
15. The surface emitting laser driving device according to claim 13, wherein the surface emitting laser driving device is provided. The pulse voltage supply means is a capacitor connected in series with the first capacitor in synchronization with the surface emitting laser being turned on, and supplies a pulse voltage to the surface emitting laser together with the first capacitor. 16. The surface emitting laser driving device according to claim 15, further comprising two capacitors.

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