JP2017139704A - Driving device for light emitting unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving device capable of changing a high voltage for driving a light emitting unit at high speed.SOLUTION: The driving device of a light emitting unit includes: a first generating unit capable of generating a first voltage; an acquiring unit that acquires charging information related to a charging period and discharging information indicating a timing of starting discharge; and a capacitor which is charged to a second voltage lower than the first voltage by the first voltage on the basis of the charge information and supplies the second voltage to the light emitting unit on the basis of the discharge information.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a technique for controlling the output of a laser.

  Laser radar devices that measure the distance from a vehicle to an object are known. Patent Document 1 discloses a power supply circuit for a laser radar device. Specifically, in Patent Document 1, first, a current is supplied from a DC power supply to an inductor, and then a capacitor is charged with magnetic energy accumulated in the inductor. After the capacitor is charged to a predetermined voltage value (VR: design value determined by circuit resistance values R7 and R8: see paragraph 0094), the inductor is disconnected from the DC power supply, and then the capacitor is discharged to supply current to the LD. Supply. When the capacitor is completely discharged, the current flowing through the LD becomes 0, so that a pulsed current flows through the LD, and as a result, a pulsed laser beam is emitted from the LD (see paragraph 0013).

JP 2010-139295 A

  In a recent lidar (LiDAR: Light Detection And Ranging), there is a case where the output of a laser diode (LD) is desired to be changed depending on, for example, the surrounding environment. However, in Patent Document 1, since the output value of the LD is fixed to a predetermined design value determined by circuit constants, in the above case, the output of the LD is changed according to the surrounding environment. Can not do it.

  In addition, when changing the output of the LD, it may be possible to change the power supply voltage of a large book, but it is difficult to design to change the voltage of a power supply that requires a high voltage such as a lidar at high speed. .

  Examples of the problem to be solved by the present invention include the above. An object of this invention is to provide the drive device which can change the high voltage which drives a light emission part at high speed.

  The invention according to claim 1 is a driving device of the light emitting unit, the first generation unit capable of generating the first voltage, the charging information related to the charging period, and the discharging information indicating the timing to start discharging. Based on the charging information, the first generating unit is charged to a second voltage lower than the first voltage, and the light emitting unit is And a capacitor for supplying electric charges charged by the second voltage.

It is a block diagram which shows the structure of the transmission / reception part of the lidar which concerns on an Example. The configuration of the transmitter is shown. The drive waveform of a laser diode is shown. The drive waveform when the output power of the laser diode LD is changed is shown. A circuit configuration example of a high voltage generation circuit and a transmitter is shown. 6 shows drive waveforms of the circuit shown in FIG. It is a graph which shows the relationship between a charging period and a charging voltage. It is a graph which shows the relationship between a charging period, an output voltage, and a peak voltage. 6 shows drive waveforms in a modification of the circuit shown in FIG.

  In a preferred embodiment of the present invention, the driving device of the light emitting unit includes a first generation unit capable of generating the first voltage, charging information related to the charging period, and discharging information indicating timing to start discharging. Based on the acquisition information to be acquired and the charging information, the first generation unit is charged to a second voltage lower than the first voltage, and based on the discharge information, the second light is supplied to the light emitting unit. And a capacitor for supplying an electric charge charged by the voltage.

  The driving device for the light emitting unit is supplied with electric charge from the first generation unit, and receives charging information and discharging information. The capacitor of the driving device is charged to the second voltage based on the charging information, and supplies the electric charge charged based on the discharging information to the light emitting unit. As a result, the light emitting unit is driven.

  One aspect of the driving device of the light emitting unit includes a second generation unit that changes the charging information according to a target output power of the light emitting unit. Thereby, a light emission part can be light-emitted with the power according to target output power.

  According to another aspect of the driving device for the light emitting unit, the charging information is generated based on voltage information to be applied to the light emitting unit, a capacitance of the capacitor, and the first voltage. A generation unit is provided. In this aspect, charging information related to the charging period is generated based on the voltage information to be supplied to the light emitting unit, the capacitance of the capacitor, and the first voltage. In a preferred example, the first generator is a charge pump circuit.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[Configuration of transceiver unit]
FIG. 1 is a block diagram illustrating a configuration of a transmission / reception unit of a rider according to an embodiment. The rider according to the present embodiment performs distance measurement of an object in all horizontal directions. The rider is used, for example, as a part of an advanced driving system for the purpose of assisting recognition of the surrounding environment of the vehicle. Specifically, the transmission / reception unit of the lidar emits a pulse laser in all horizontal directions while changing the emission direction, receives the reflected light of the pulse laser reflected by the target, and receives the signal as a signal processing unit (DSP). ).

  As shown in FIG. 1, the transmission / reception unit of the rider includes a control unit 10, a high voltage generation circuit 11, a transmitter 12, a power supply 13, a scanner 14, a power supply 16, a receiver 17, a high voltage power supply 18, and A / D converter 19.

  The control unit 10 receives a laser output instruction signal. The output instruction signal is a signal that instructs an output intensity, an emission direction, and an emission timing of a laser Lt described later. Various methods are assumed as the laser emission method by the lidar, and the output intensity of the laser is determined according to the method. For example, when measuring a target whose approximate position is known based on map data, etc., a laser is output with an intensity corresponding to the distance to the target within the estimated range of the target. To do. On the other hand, when searching for the presence or absence of an unknown target, the laser is emitted over a wide range, for example, while changing the intensity at a plurality of levels. The control unit 10 receives an output instruction signal determined according to such various situations. Then, the control unit 10 outputs an external signal (enable signal) En to the high voltage generation circuit 11 and outputs a trigger pulse Tp to the transmitter 12.

  The high voltage generation circuit 11 generates a high voltage Vh and supplies it to the transmitter 12. In addition to this, the transmitter 12 is supplied with the voltage Vcc from the power supply 13. The transmitter 12 includes a laser diode (LD) and an LD driver. The transmitter 12 outputs the pulse laser Lt to the scanner 14 based on the high voltage Vh supplied from the high voltage generation circuit 11 and the trigger pulse Tp supplied from the control unit 10. Details of the transmitter 12 will be described later.

  The scanner 14 includes a transmission optical system and a reception optical system, scans the pulse laser Lt output from the transmitter 12 within a predetermined range, and receives the reflected light Lr obtained by reflecting the emitted pulse laser Lt at the target. To the receiver 17. The scanner 14 includes an optical system and a motor for rotating the optical system.

  The receiver 17 is supplied with a power supply voltage Vcc from a power supply 16 and a high voltage VH from a high-voltage power supply 18. The receiver 17 includes, for example, a light receiving element such as an avalanche photodiode and a current-voltage conversion circuit such as a transimpedance amplifier. The light receiving element generates a weak current corresponding to the amount of the reflected light Lr guided by the scanner 14. The current-voltage conversion circuit amplifies the weak current supplied from the light receiving element, converts it into a voltage signal, and outputs it to the A / D converter 19.

  The A / D converter 19 converts the voltage signal supplied from the receiver 17 into a digital signal and supplies it to the signal processing unit (DSP).

[Transmitter configuration]
FIG. 2 shows the configuration of the transmitter 12. As illustrated, the transmitter 12 includes a switch M1 formed of an FET, resistors Rchg, Rlim, and Rm, a capacitor Cchg, a diode Dclp, and a laser diode LD. In practice, an FET driver is provided to drive the switch M1, and the power supply voltage Vcc supplied from the power supply 13 is supplied to the FET driver, but the FET driver is not shown in FIG.

  The transmitter 12 basically applies the high voltage Vh supplied from the high voltage generation circuit 11 to charge the capacitor Cchg, and instantaneously discharges the charge charged in the capacitor Cchg through the switch M1 and flows it to the laser diode LD. As a result, the pulse laser Lt is emitted. As an example, the capacitor Cchg is charged to several tens to one hundred and several tens of volts, and then discharged at several tens of amperes.

  Specifically, first, at the time of charging, the high voltage Vh is supplied from the high voltage generation circuit 11, and the switch M1 is turned off by the trigger pulse Tp. As a result, the capacitor Cchg is charged with the high voltage Vh through the resistor Rchg as indicated by the broken charging path 31. At the time of discharging, the switch M1 is turned on by the trigger pulse Tp. As a result, the electric charge stored in the capacitor Cchg is instantaneously discharged as indicated by the broken discharge path 32, and the laser diode LD emits light.

  In the above configuration, the high voltage generation circuit 11 corresponds to the first generation unit of the present invention, the transmitter 12 corresponds to the acquisition unit of the present invention, the laser diode LD corresponds to the light emitting unit of the present invention, and the capacitor Cchg This corresponds to the capacitor of the invention. The control unit 10 corresponds to the second generation unit and the third generation unit of the present invention.

[Driving method]
Next, a method of driving the laser diode LD by the control unit 10, the high voltage generation circuit 11, and the transmitter 12 will be described. FIG. 3 shows a timing chart of the driving waveform of the laser diode.

  The high voltage generation circuit 11 has a function of switching the output based on an external signal (enable signal) En. Specifically, the high voltage generation circuit 11 supplies charges to the transmitter 12 during a period in which the external signal En is at a high level (hereinafter simply referred to as “H”), and the external signal En is low. No charge is supplied to the transmitter 12 during the level (hereinafter simply referred to as “L”) period. That is, the high voltage generation circuit 11 supplies electric charges to the transmitter 12 only when the external signal En is “H”. For this reason, as shown in FIG. 3, the capacitor Cchg of the transmitter 12 is charged only during the period when the external signal En is “H”. As shown in FIG. 2, the charging voltage Vc indicates the charging voltage of the capacitor Cchg.

  The trigger pulse Tp is a trigger signal for discharging the capacitor Cchg, and becomes “H” only at the discharge timing. Therefore, as shown in FIG. 3, the control unit 10 charges the capacitor Cchg by setting the trigger pulse Tp to “L” and the external signal En to “H”. Then, the control unit 10 sets the external signal En to “L” at the timing when the desired charge is accumulated, and sets the trigger pulse Tp to “H”, thereby causing the laser diode LD to emit light, and causing the laser pulse Lt to be emitted. Output.

  As shown in the waveform of the charging voltage Vc in FIG. 3, the capacitor Cchg is charged toward the high voltage Vh in the charging period tc in which the external signal En is “H” and the trigger pulse Tp is “L”. To go. The discharge amount at the discharge timing is determined by the charge amount (charge amount charged) of the capacitor Cchg at that time. Therefore, in order to change the output power of the laser diode LD, the charge amount of the capacitor Cchg, that is, the charging period tc may be changed.

  FIG. 4 shows an example in which the output power of the laser diode LD is changed. 4A is a timing chart of the drive waveform when the output power of the laser diode LD is increased, and FIG. 4B is a timing chart of the drive waveform when the output power of the laser diode LD is decreased. . As shown in FIG. 4A, when the charging period tc, that is, the period in which the external signal En is set to “H” is lengthened, the charging voltage Vc (= V1) of the capacitor Cchg increases, and as a result, the laser diode LD The output power P1 increases. On the other hand, when the charging period tc is shortened, the charging voltage Vc (= V2 <V1) of the capacitor Cchg is reduced, and as a result, the output power P2 (<P1) of the laser diode LD is also reduced. Therefore, the control unit 10 can change the output power of the laser diode LD by controlling the charging period tc by controlling the external signal En.

  Next, features of the driving method of this embodiment will be described. As described above, the driving method of the present embodiment is characterized in that the charging period tc of the capacitor Cchg is changed using the rising characteristics of the high voltage generation circuit 11 and the output power of the pulse laser Lt is changed. . This is because it is not necessary to always apply a stable high-voltage DC voltage to the drive circuit in the transmitter 12. That is, it is based on the idea that the charge necessary for the capacitor Cchg should be accumulated at the moment of outputting the pulse laser. For this reason, in this embodiment, the capacitor Cchg is charged for the charging period tc corresponding to the required output power, and then discharged to output the pulse laser with the required power.

  Further, the rising characteristic (transient characteristic) when charging the capacitor Cchg is determined by the load on the high voltage generation circuit 11, that is, the constant of the drive circuit. In this embodiment, the load on the high voltage generation circuit 11 is known. Since only the charging capacitor Cchg is basically used, it is possible to grasp in advance the rising characteristics when charging the capacitor Cchg. That is, since the transient characteristic of the charging voltage Vc is known, the charging period tc can be determined based on the target output power of the laser diode LD. Therefore, the control unit 10 outputs the external signal at a time that is back by the charging period tc necessary for obtaining the target output power from the emission timing of the desired laser pulse Lt (that is, the timing at which the trigger pulse Tp is set to “H”). En may be set to “H”, and the output of the pulse laser can be changed at high speed by simple control.

Furthermore, the driving method of this embodiment has the following characteristics.
-Cost reduction Normally, a high voltage generation circuit and a high voltage power supply circuit require a control circuit for stabilizing the output voltage. In general, a circuit made as a power supply is added with a circuit that feeds back and stabilizes the output voltage so that the output voltage does not fluctuate with respect to load fluctuations. However, in this embodiment, since the load of the high voltage generation circuit 11 does not fluctuate as described above, a control circuit for stabilizing the output voltage becomes unnecessary, and the cost can be reduced.

Reduction of energy consumption Normally, the high voltage generation circuit and the high voltage power supply circuit are configured by switching circuits, but in this embodiment, the high voltage generation circuit 11 should not be switched during the non-charging period of the capacitor Cchg. Therefore, unnecessary switching loss can be suppressed and energy consumption can be reduced.

-Low noise As described above, during the non-charging period of the capacitor Cchg, switching can be prevented from being performed by the high-voltage generation circuit 11, and thus switching noise can be suppressed during that period. In particular, after the pulse laser is output, the receiver 17 receives the reflected light Lr. Therefore, it is beneficial to reduce the influence of switching noise on the receiver 17.

[Circuit configuration example]
FIG. 5 shows a circuit configuration example of the high voltage generation circuit 11 and the transmitter 12. In FIG. 5, the high voltage generation circuit 11 is configured as a charge pump circuit (Dickson Charge Pump), and a clock CK is input in addition to the external signal En. The transmitter 12 is basically the same as the configuration shown in FIG. 2 except that the resistor Rin and the FET driver 33 are shown.

  FIG. 6 is a timing chart of drive waveforms of the circuit shown in FIG. The period in which the external signal En is “H” and the trigger pulse Tp is “L” is the charging period tc. Thereafter, when the trigger pulse Tp rises to “H”, the capacitor Cchg is discharged, and the pulse laser Lt is output from the laser diode LD.

  FIG. 7A is a graph showing a charging waveform when the charging period tc of the capacitor Cchg is changed. The horizontal axis indicates the charging period tc, and the vertical axis indicates the charging voltage Vc. The longer the charging period tc, the higher the charging voltage Vc of the capacitor Chg. FIG. 7B is a graph showing the relationship between the charging period tc and the charging voltage Vc of the capacitor Cchg. The charging voltage Vc increases as the charging period tc increases.

  FIG. 8A is a graph showing the optical output waveform of the pulse laser emitted from the laser diode LD when the charging period tc is changed. It can be seen that the output power increases as the charging period tc increases. FIG. 8B is a graph showing the relationship between the charging period tc and the peak power of the optical output from the laser diode LD. It can be seen that the peak power of the pulse laser output from the laser diode LD increases as the charging period tc increases.

  7 and 8, it can be confirmed that in this circuit example, the light output from the laser diode LD can be controlled by controlling the timing of the trigger pulse Tp and the external signal En.

  The transient characteristic of the output voltage Vc of the high voltage generation circuit 11 (n-stage charge pump circuit) in the circuit example of FIG. 5 is ideally obtained by the following equation, where the charging period is tc.

  As can be seen from the equation (1), the rising characteristics can be controlled by changing the switching frequency of the charge pump circuit.

  Based on the equation (1), in order to obtain the required charging voltage Vc, it is only necessary to calculate how much the charging period tc is necessary and to create a table or the like in advance and store it in the memory. The control unit 10 may refer to the table to obtain the charging period tc necessary for obtaining the target output power and generate the external signal En and the trigger pulse Tp. Note that the table may be created by obtaining the relationship between the charging period tc and the charging voltage Vc through experiments or the like, instead of based on the above theoretical formula.

  By configuring the high-voltage generation circuit 11 with a charge pump circuit as in the above circuit example, (1) the configuration is simplified, and (2) no inductor is used, so there is no unnecessary radiation and low noise is achieved. (3) Since an inductor is not used, advantages such as the possibility of reducing the mounting area can be obtained.

  FIG. 9 shows a timing chart of drive waveforms in a modification of the circuit shown in FIG. As shown in the figure, the function of the external signal (enable signal) En may be included in the clock signal CKx. In this case, the AND circuit 41 of the high voltage generation circuit 11 of FIG. 5 may be deleted, and the clock signal CKx shown in FIG. 10 may be input instead of the output of the AND circuit 41. In this modification, since the external signal En can be reduced, the circuit configuration can be simplified accordingly.

DESCRIPTION OF SYMBOLS 10 Control part 11 High voltage generation circuit 12 Transmitter 14 Scanner 17 Receiver 19 A / D converter

Claims (4)

A first generator capable of generating a first voltage;
An acquisition unit that acquires charge information related to a charge period and discharge information indicating a timing to start discharging;
Based on the charging information, the first generator is charged to a second voltage lower than the first voltage, and the light emitting unit is charged with the second voltage based on the discharge information. A driving device for a light emitting unit, comprising a capacitor for supplying electric charge.   The driving device of the light emitting unit according to claim 1, further comprising a second generation unit that changes the charging information according to a target output power of the light emitting unit.   3. A third generation unit that generates the charging information based on voltage information to be supplied to the light emitting unit, a capacitance of the capacitor, and the first voltage. 4. The drive unit of the light emission part as described in 2.   4. The light emitting unit driving device according to claim 1, wherein the first generation unit is a charge pump circuit. 5.