JP2023180193A - Light-emitting device - Google Patents

Abstract

To provide a light-emitting device capable of lighting multiple light sources with a simple configuration.SOLUTION: A light-emitting device includes n light sources (n≥2), n power supply circuits respectively provided for the n light sources, and a switch installed between a ground side node of each of the n light sources and the ground, and the power supply circuit generates a power supply voltage for a corresponding one of the n light sources on the basis of the first signal, stops generation of the power supply voltage on the basis of a second signal, and the switch is turned on on the basis of a turn-on instruction and turned off on the basis of a turn-off instruction while the power supply voltage for the one light source is being generated.SELECTED DRAWING: Figure 4

Description

The present invention relates to a light emitting device.

Measuring devices that measure the distance to an object based on light emitted from a light emitting element such as a laser diode are generally provided with a drive circuit that drives the light emitting element (for example, Patent Document 1) .

JP2021-28924A

Since the drive circuit disclosed in Patent Document 1 is provided with a level shift circuit, the structure of the drive circuit is generally complicated.

The present invention has been made in view of the conventional problems as described above, and an object thereof is to provide a light emitting device that can light a plurality of light sources with a simple configuration.

One aspect of the present invention includes n light sources (n≧2), the n power supply circuits provided for each of the n light sources, and a ground-side node of each of the n light sources. , and a switch provided between ground and the power supply circuit, the power supply circuit generates a power supply voltage for a corresponding one of the n light sources based on the first signal, and generates a power supply voltage for a corresponding one of the n light sources based on the first signal, and the light emitting device, wherein the switch is turned on based on a turn-on instruction and turned off based on a turn-off instruction while the power supply voltage for the one light source is being generated; It is.

According to the present invention, it is possible to provide a light emitting device that can light up a plurality of light sources with a simple configuration.

1 is a diagram showing an example of a measuring device 10. FIG. It is a figure showing an example of light emitting device 20a. It is a figure showing an example of the composition of light source D0. It is a figure showing an example of light emitting device 20b. FIG. 3 is a diagram for explaining signals S10 to S19. FIG. 3 is a diagram for explaining the operation of the light emitting device 20b. It is a figure showing an example of a current waveform of light emitting device 20b. It is a diagram showing an example of a light emitting device 20c. It is a figure showing an example of a current waveform of light emitting device 20c.

From the description of this specification and the attached drawings, at least the following matters will become clear. In addition, here, the same or equivalent components, members, etc. shown in each drawing are denoted by the same reference numerals, and redundant explanations are omitted as appropriate.

=====This embodiment =====
<<Overview of measuring device 10>>
The measuring device 10 has a function as so-called LiDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging), and is a device that measures the distance to the target object 11. Specifically, the measuring device 10 measures the distance to the object 11 based on the TOF method (Time of Flight), which emits measurement light and detects the reflected light reflected from the surface of the object 11. . Further, the measuring device 10 is installed, for example, in a vehicle (not shown), and includes a light emitting device 20, a light receiving device 21, and a control device 22.

The target object 11 is, for example, a vehicle different from the vehicle in which the measuring device 10 is installed, a person, or a structure such as a street light or a building.

The light emitting device 20 emits measurement light to the object 11 based on control from a control device 22 (described later). Note that details of the light emitting device 20 will be described later.

The light receiving device 21 receives reflected light from the object 11 and outputs information regarding the reflected light (for example, timing and level) to the control device 22 .

The control device 22 is a device that centrally controls the measuring device 10. Specifically, the control device 22 controls the emission of measurement light from the light emitting device 20, and measures the distance to the object 11 based on the output from the light receiving device 21 using the TOF method (Time of Flight). do. Although not shown here, the control device 22 includes, for example, a storage device and an arithmetic device that executes a program stored in the storage device.

<<Details of the light emitting device 20a>>
FIG. 2 is a diagram showing an example of the configuration of a general light emitting device 20a. The light emitting device 20a includes light sources D0 to D9, a capacitor 40, power circuits 50 to 59, and a control circuit 60. Note that in FIG. 2, for convenience, some components of the light emitting device 20a (light sources D2 to D8 and power supply circuits 52 to 58) are omitted.

==About the light source==
The light source D0 includes, for example, a vertical cavity surface emitting laser that can emit measurement light in an infrared region. Specifically, the light source D0 includes, for example, 16 laser diodes 100 to 115 and an optical member 120 that adjusts the light distribution of the light from the laser diodes 100 to 115, as illustrated in FIG. configured.

The cathodes of each of the laser diodes 100-115 are common, and the anodes of each of them are also common. Therefore, the light emitted from each of the laser diodes 100 to 115 becomes measurement light from one light source D0. Here, the light source D0 includes 16 laser diodes 100 to 115, but the number may be other (for example, 8 or 32).

The optical member 120 is, for example, an optical diffusing element (LSD: Light Shaping Diffuser), and diffuses the light emitted from each of the laser diodes 100 to 115 so that the light distribution from the light source D0 becomes desired ( In other words, it is a member (to be adjusted). Although an LSD is used here as the optical member 120, any member may be used as long as it can distribute the light from the light source D0 in a desired pattern.

Each of the light sources D1 to D9 includes the same surface-emitting laser (hereinafter simply referred to as "VCSEL") and an optical member 120 as the light source D0, so a detailed description thereof will be omitted here. Further, the nine light sources D0 to D9 correspond to "n (n is an integer of 2 or more)" light sources. Further, hereinafter, the light source D0 may be described as a VCSEL for convenience.

==About capacitor 40==
The capacitor 40 is an element for stabilizing a predetermined power supply voltage Vdd1 (for example, several tens of V) supplied to the power supply circuits 50 to 59. A predetermined power supply voltage Vdd1 is applied to the capacitor 40.

==Details of power supply circuit 50==
The power supply circuit 50 is a circuit that generates a power supply voltage V0 for lighting the light source D0 based on the power supply voltage Vdd1 and the signal S0 from the control circuit 60. Specifically, the power supply circuit 50 generates the power supply voltage V0 when a high level (hereinafter referred to as "H level") signal S0 is input from the control circuit 60 to turn on the light source D0. On the other hand, when the power supply circuit 50 receives a low level (hereinafter referred to as "L level") signal S0 from the control circuit 60 to turn off the light source D0, it stops generating the power supply voltage V0.

The power supply circuit 50 includes a diode 200, a capacitor 201, a buffer 210, a transformer 211, an integrated circuit (IC) 212, and a resistor 213.

The diode 200, together with the capacitor 201, is an element that generates a power supply voltage for operating an IC 212 (described later). A power supply voltage Vdd2 (eg, 5V) is applied to the anode of the diode 200, and the cathode of the diode 200 is connected to the capacitor 201.

When the capacitor 201 is charged with the current from the diode 200, a power supply voltage for operating the IC 212 is generated.

Buffer 210 outputs signal Sa0 having the same logic level as signal S0 to transformer 211. Specifically, the buffer 210 outputs the H level signal Sa0 based on the H level signal S0, and outputs the L level signal Sa0 based on the L level signal S0. Here, the signal S0 is a signal for controlling on/off of a driving transistor 231 (described later) of the IC 212, and the L level of the signal S0 is, for example, 0V, and the H level is, for example, 3V.

The transformer 211 is an insulated transformer that converts and outputs the DC level while maintaining the amplitude of the input signal, and includes a primary coil 220 and a secondary coil 221 that is electromagnetically coupled to the primary coil 220. It consists of:

Here, the transformer 211 functions as a so-called level shift circuit. Therefore, the transformer 211 converts the signal Sa0, whose logic level changes with respect to the ground voltage (0V), into the signal Sb0, which changes with the power supply voltage V0 as a reference. In other words, the transformer 211 causes the secondary coil 221 to generate the H level signal Sb0 when the signal Sa0 is at the H level, and causes the secondary coil 221 to generate the L level signal Sb0 when the signal Sa0 is at the L level. let

Although the transformer 211 is used here as a so-called level shift circuit, the present invention is not limited to this, and other configurations (for example, a circuit including a photocoupler or the like) may be used.

The IC 212 generates the power supply voltage V0 to the light source D0 when the signal Sb0 from the secondary coil 221 is at the H level, and stops generating the power supply voltage V0 when the signal Sb0 is at the L level. The IC 212 includes a buffer 230 and a driving transistor 231.

The buffer 230 outputs a signal at the same logic level as the signal Sb0 to the driving transistor 231. Specifically, when the secondary coil 221 outputs the H level signal Sb0, the buffer 230 outputs the H level signal to the driving transistor 231. As a result, the driving transistor 231 is turned on.

On the other hand, when the secondary coil 221 outputs the L level signal Sb0, the buffer 230 outputs the L level signal to the driving transistor 231. As a result, the driving transistor 231 is turned off.

Here, when the driving transistor 231 is turned on, the power supply voltage V0 of the line L0 on the anode side of the light source D0 rises to approximately the power supply voltage Vdd1. Since the high level power supply voltage V0 is applied to the line L0 on the anode side of the light source D0, the light source D0 is turned on (emits measurement light).

Note that the resistor 213 is an element for limiting the current flowing to the light source D0. Further, when the driving transistor 231 is turned on, the voltage of the line L0 to which the source electrode of the driving transistor 231 is connected rises to approximately the power supply voltage Vdd1 (for example, several tens of V). Therefore, in order to maintain the on state of the driving transistor 231, it is necessary to continue applying a voltage higher than the threshold of the driving transistor 231 from the voltage of the line L0 to the gate electrode of the driving transistor 231.

In the power supply circuit 50 of FIG. 2, the transformer 211 shifts the DC level of the signal Sa0 and outputs it to the secondary side as the signal Sb0. Therefore, the logic level (H level or L level) of the signal Sb0 on the secondary side of the transformer 211 changes with reference to the voltage of the line L0. As a result, in the power supply circuit 50, the driving transistor 231 can be turned on or off based on the signal S0 that changes with respect to the ground voltage (0V).

Note that when the signal S0 becomes L level and the driving transistor 231 is turned off, the power supply circuit 50 stops generating the power supply voltage V0. As a result, the supply of the power supply voltage V0 to the light source D0 is also stopped, so the light source D0 is turned off.

== Regarding power supply circuits 51 to 59 ==
Like the power supply circuit 50, each of the power supply circuits 51 to 59 generates power supply voltages V1 to V9 for the light sources D1 to D9 based on the signals S1 to S9. Therefore, detailed explanation of the power supply circuits 51 to 59 will be omitted here.

==About the control circuit 60==
The control circuit 60 controls each of the power supply circuits 50 to 59 so that the light sources D0 to D9 are sequentially lit based on a lighting start instruction from the control device 22 of FIG. Here, "the light sources D0 to D9 are turned on in sequence" means that among the 10 light sources D0 to D9, for example, the light sources are turned on one by one in the order of light sources D0, D1...D9. . Therefore, among the light sources D0 to D9, for example, when the light source D0 is lit, the other light sources D1 to D9 are off, and for example, when the light source D1 is lit, the light source D0 is turned off. , D2 to D9 are off.

Therefore, among the signals S0 to S9, the control circuit 60 sets the level of one signal corresponding to the light source to be turned on to the H level, and sets the levels of the other nine signals to the L level. By outputting such signals S0 to S9, the light sources D0 to D9 are sequentially turned on.

Incidentally, each of the power supply circuits 50 to 59 of the light emitting device 20a in FIG. 2 includes a large number of components such as a transformer 211 and an IC 212. Therefore, in general, the mounting space occupied by the power supply circuits 50 to 59 becomes larger in the light emitting device 20a.

Furthermore, since the transformer 211 that level-shifts the signal S0 and the capacitor 201 that generates the power supply voltage of the buffer 230 include relatively large parasitic inductors and parasitic capacitances, the accuracy of the power supply voltage V0 of the light source D0 may deteriorate. . Therefore, the measuring device 10 of this embodiment uses a light emitting device 20b that operates with a simple configuration.

<<Details of light emitting device 20b>>
The light emitting device 20b shown in FIG. 4 is a device that lights up the light sources D0 to D9 based on a lighting start instruction from the control device 22, and includes the light sources D0 to D9, the capacitor 40, the IC 41, the power supply circuits 70 to 79, and the control device 20b. It is configured to include a circuit 80. Note that the structures denoted by the same reference numerals in FIG. 4 and FIG. 2 are the same. Therefore, the IC 41, power supply circuits 70 to 79, and control circuit 80 will be mainly described here. Note that in FIG. 4, for convenience, some components of the light emitting device 20b (light sources D2 to D8 and power supply circuits 72 to 78) are omitted.

==About IC41==
The IC41 is a circuit that lights up the light source to which a power supply voltage is applied among the light sources D0 to D9. The IC 41 of this embodiment is provided between the ground and the ground side node of each of the light sources D0 to D9. Note that the "ground side node of the light source D0" is, for example, a node to which the cathodes of the laser diodes 100 to 115 constituting the light source D0 are connected.

The IC 41 is a circuit similar to the IC 212 in FIG. 2, and includes a buffer 300 and a driving transistor 301.

Like the buffer 230, the buffer 300 outputs a signal having the same logic level as the input signal to the driving transistor 301. In this embodiment, a signal S20 from a control circuit 80 (described later) is input to the buffer 300. Therefore, the buffer 300 turns on the driving transistor 301 based on the H level signal S20, and turns off the driving transistor 301 based on the L level signal S20.

Note that the H level signal S20 corresponds to a "lighting instruction" to turn on the light source, and the L level signal S20 corresponds to a "lighting out instruction" to turn off the light source.

The driving transistor 301 has a drain electrode connected to a node on the ground side of the light sources D0 to D9, and a source electrode grounded. Therefore, when the driving transistor 301 is turned on, a current flows to the light source to which the power supply voltage is applied among the light sources D0 to D9, and the light source is turned on. Note that when the driving transistor 301 is turned off, the current path from the light sources D0 to D9 to the ground is cut off, so all of the light sources D0 to D9 are turned off.

The driving transistor 301 of this embodiment corresponds to a "switch". In this embodiment, a Ga (gallium nitride) N-type FET (Field effect transistor) is used as the drive transistor 301 as a "switch", but other compound transistors, general MOS transistors, A bipolar transistor may also be used.

==Details of power supply circuit 70==
The power supply circuit 70 is a circuit that generates a power supply voltage V10 for lighting the light source D0 based on the signal S10. Specifically, the power supply circuit 70 generates the power supply voltage V10 when the H level signal S10 is input, and stops generating the power supply voltage V10 when the L level signal S10 is input.

The power supply circuit 70 includes a buffer 310, a PMOS transistor 311, an NMOS transistor 312, a resistor 313, and a capacitor 314.

Buffer 310 operates as an inverter that outputs signal Sc0, which is the logic level of signal S10 inverted. Therefore, the buffer 310 outputs the L level signal Sc0 based on the H level S10, and outputs the H level signal Sc0 based on the L level S10.

The gate electrode of the PMOS transistor 311 and the gate electrode of the NMOS transistor 312 are connected, and the drain electrode of the PMOS transistor 311 and the drain electrode of the NMOS transistor 312 are connected. Therefore, the PMOS transistor 311 and the NMOS transistor 312 constitute a so-called push-pull circuit.

In this embodiment, when the signal Sc0 becomes L level, the PMOS transistor 311 is turned on and the NMOS transistor 312 is turned off. As a result, the capacitor 314 is charged and rises to approximately the power supply voltage Vdd1 (for example, several tens of V).

Further, when the signal Sc0 becomes H level, the PMOS transistor 311 is turned off and the NMOS transistor 312 is turned on, so that the capacitor 314 is discharged. Note that at this time, the charging voltage of the capacitor 314 decreases to approximately 0V.

Here, in this embodiment, one end of the capacitor 314 is connected to the anode of the light source D0 via the line L10. Therefore, the charging voltage of the capacitor 314 becomes the power supply voltage V10 generated by the power supply circuit 70.

In this way, the power supply circuit 70 can generate the power supply voltage V10 for lighting the light source D0 or stop generating the power supply voltage V10, based on the logic level of the signal S10.

Note that in this embodiment, the buffer 310, the PMOS transistor 311, and the NMOS transistor 312 correspond to a "charging and discharging circuit" that charges and discharges the capacitor 314. Further, the resistor 313 provided between the push-pull circuit described above and the capacitor 314 is an element that limits the current that charges and discharges the capacitor 314. Further, the power supply circuit 70 corresponds to a circuit that generates a power supply voltage V10 for "one corresponding light source D0" among the light sources D0 to D9. Further, the capacitor 314 corresponds to a "first capacitor".

== Regarding power supply circuits 71 to 79 ==
Like the power supply circuit 70, each of the power supply circuits 71 to 79 generates power supply voltages V11 to V19 for the light sources D11 to D19 based on the signals S11 to S19. Therefore, detailed explanation of the power supply circuits 71 to 79 will be omitted here. Note that in this embodiment, the power supply circuits 70 to 79 are provided for each of the light sources D0 to D9.

==About the control circuit 80==
The control circuit 80 controls each of the power supply circuits 70 to 79 so that the light sources D0 to D9 can be sequentially turned on based on a lighting start instruction from the control device 22 of FIG. Specifically, among the signals S10 to S19, the control circuit 80 sets the level of the signal sent to the power supply circuit corresponding to the light source to be turned on to the H level, and sets the level of the other nine signals to the L level.

Further, when a lighting start instruction is input, the control circuit 80 outputs an H level signal S20 (lighting instruction) at the timing to turn on the target light source, and outputs an L level signal S20 (lighting out instruction) at the timing to turn off the target light source. ) is output.

==Operation of control circuit 80 and main waveforms of light emitting device 20b==
FIG. 5 is a diagram showing an example of waveforms of signals S10 to S19. FIG. 6 is a diagram showing an example of main waveforms of the light emitting device 20b when the light source D0 is turned on. Note that in FIG. 5, only the signals S10, S11, and S19 are illustrated for convenience.

First, the control circuit 80 in FIG. 4 changes the signal S10 from the L level to the H level at time t0, so the power supply circuit 70 starts generating the power supply voltage V10. As a result, as shown in FIG. 6, power supply voltage V10 rises from 0V to the level of power supply voltage Vdd1. Note that, in reality, the power supply voltage V10 rises with a slight delay from the rising edge of the signal S10 to the commercial device t0, but the delay is omitted here for convenience.

Further, the control circuit 80 sets each of the signals S11 to S19 to the L level at time t0. Therefore, generation of power supply voltages V11 to VB19 of power supply circuits 71 to 79 is stopped.

At time t1 (see FIG. 6), when a predetermined period Ta has elapsed from time t0, the control circuit 80 outputs an H-level signal S20 to turn on the light source D0. As a result, the driving transistor 301 of the IC 41 in FIG. 4 is turned on. Therefore, the current I0 flows through the light source D0, and the light source D0 is turned on.

In this embodiment, the predetermined period Ta is longer than the period during which the level of the power supply voltage V10 changes from 0V to the power supply voltage Vdd1. Further, when the current I0 flows through the light source D0, the capacitor 40 is discharged, so that the power supply voltage V10 decreases from the level of the power supply voltage Vdd1.

Then, at time t2 in FIG. 6, the control circuit 80 changes the signal S20 to L level in order to turn off the light source D0. As a result, the driving transistor 301 is turned off. Therefore, the current I0 of the light source D0 is cut off, so that the light source D0 is turned off. Note that at time t2, the current I0 is cut off and the discharge of the capacitor 40 is stopped, so the power supply voltage V10 rises to the power supply voltage Vdd1.

Then, at time t3, the control circuit 80 turns on the light source D0 again in order to change the signal S20 to H level. Note that in this embodiment, the operation from time t3 to time t1 to t2 is repeated four times. Note that while the light source D0 is turned on five times while the power supply voltage V10 is being generated, the number of times the light source D0 is turned on is merely an example.

Furthermore, at time t11, the control circuit 80 changes the signal S10 to L level in order to stop generating the power supply voltage V10. As a result, the capacitor 314 in FIG. 4 is discharged via the resistor 313 and the NMOS transistor 312, so the power supply voltage V10 gradually decreases. Note that, in reality, the power supply voltage V10 drops with a slight delay from the fall timing t11 of the signal S10, but the delay is omitted here for convenience.

Further, as shown in FIG. 5, at time t11, the control circuit 80 changes the signal S11 to H level in order to generate the power supply voltage V11. As a result, the capacitor 314 (not shown) of the power supply circuit 71 is gradually charged, so that the power supply voltage V11 increases.

In this embodiment, for example, as shown at time t11 in FIG. 5, the timing at which discharging of the capacitor 314 of the power supply circuit 70 is started and the timing at which charging of the capacitor 314 (not shown) of the power supply circuit 71 is started is determined. are the same. That is, in this embodiment, the control circuit 80 controls the power supply circuits 70 and 71 so that the capacitor 314 (not shown) of the power supply circuit 71 is charged while the capacitor 314 of the power supply circuit 70 is being discharged. .

Incidentally, it is also possible to start charging the capacitor 314 (not shown) of the power supply circuit 71 after the capacitor 314 of the power supply circuit 70 is discharged and the power supply voltage V10 becomes approximately 0V. However, in such a case, since the signal S11 becomes H level after time t12 in FIGS. 5 and 6, the timing of turning on the light source D1 will also be delayed.

In this embodiment, when the capacitor 314 of the power supply circuit 70 is being discharged (that is, during the period when the level of the power supply voltage V10 is lowered and higher than 0V), charging of the capacitor 314 of the power supply circuit 71 to be turned on next starts. has been done. Therefore, in this embodiment, it is possible to turn on the light source at shorter intervals.

Although not shown in FIG. 5, when the above-mentioned predetermined period Ta has elapsed from time t11, the control circuit 80 transmits the H-level signal S20 to 5. times (see Figure 6). As a result, the light source D1 is also turned on five times at the same timing as the light source D0. Here, the operation when the control circuit 80 turns on the light sources D0 and D1 has been described, but the same applies to the other light sources D2 to D9.

In this way, the power supply circuit 70 of this embodiment shown in FIG. 4 does not include the diode 200, capacitor 201, transformer 211, and IC 212 included in the power supply circuit 50 of FIG. Furthermore, the light emitting device 20b controls lighting and extinguishing of the light sources D0 to D9 by providing one IC 41 between the ground side nodes of the light sources D0 to D9 and the ground. Therefore, in this embodiment, lighting of a plurality of light sources can be controlled with a simple configuration.

Note that the H level signals S10 to S19 of this embodiment correspond to "first signals", and the L level signals S10 to S19 correspond to "second signals". Further, for example, the power supply circuit 70 corresponds to a "first power supply circuit", and the power supply circuit 71 corresponds to a "second power supply circuit".

By the way, in order to increase the distance to the object 11 that can be measured by the measuring device 10 (hereinafter referred to as "measurement distance"), it is necessary to increase the intensity of the light emitted from the light source D0. Furthermore, in order to increase the intensity of the light emitted from the light source D0, it is necessary to increase the current I0 that turns on the light source D0. As described above, in the light emitting device 20b of FIG. 4, the discharge current of the capacitor 314 of the power supply circuit 70 becomes the current I0 that lights up the light source D0. Therefore, by increasing the capacitance of the capacitor 314, the measuring distance of the measuring device 10 can be increased.

However, when the capacitance of the capacitor 314 is increased, the variation among the capacitors 314 included in each of the power supply circuits 70 to 79 generally increases. FIG. 7 is a diagram showing an example of the waveforms of the currents I0 to I2 when the capacitances of the capacitors 314 of the power supply circuits 70 to 72 are set to 2200 pF, 2000 pF, and 1800 pF, respectively.

In FIG. 7, the current I0 from the 2200 pF capacitor 314 is shown by a solid line, the current I1 from the 2000 pF capacitor 314 is shown by a dotted line with wide intervals, and the current I2 from the 1800 pF capacitor 314 is shown by a narrow dotted line. Indicated by dotted lines.

Further, in FIG. 7, the timing at which the driving transistor 301 is turned on when the currents I0 to I2 are generated is shown to match time t20 so that the waveforms of the currents I0 to I2 can be compared.

Here, taking the current I0 as an example, the driving transistor 301 is turned on at time t20, so the current I0 increases. Then, when the capacitor 314 of the power supply circuit 70 is discharged, the current I0 decreases to zero. Thereafter, the driving transistor 301 is turned off at a predetermined timing. Note that although the current I0 has been explained here as an example, the same applies to the currents I1 and I2.

In this embodiment, as shown in FIG. 7, when the capacitance of the capacitor 314 is as large as 2200 pF, the peak value (approximately 18 A) of the current I0 for lighting the light source is the peak value (approximately 17 A) of each of the current values I1 and I2. 5A, approximately 17A). Therefore, in the light emitting device 20b, when the capacitors 314 with small variations are used in each of the power supply circuits 70 to 79, the light sources D0 to D9 can be turned on with high accuracy. Note that by using capacitors with relatively small capacitance values (for example, capacitors smaller than 1000 pF) for the plurality of capacitors 314, variations among the plurality of capacitors 314 can be suppressed.

<<Details of the light emitting device 20c>>
The light emitting device 20c shown in FIG. 8 is a device that can suppress variations in the currents I0 to I9 while increasing the peak values of the currents I0 to I9. The light emitting device 20c includes light sources D0 to D9, capacitors 40 and 400, an IC 41, power supply circuits 70 to 79, a control circuit 80, and a resistor 401. Note that the configurations with the same reference numerals in FIG. 8 and FIG. 4 are the same. Therefore, here, the description will focus on capacitor 400, resistor 401, and capacitor 314 included in each of power supply circuits 70 to 79.

The capacitor 400 is an element for determining the current value (in particular, the peak value) of the current I0 to I9 for lighting the light sources D0 to D9, and connects the ground side node of each of the light sources D0 to D9 and the driving transistor 301. is set between. Specifically, one end of the capacitor 400 is connected to the ground side node of each of the light sources D0 to D9, and the other end is connected to the drain electrode of the driving transistor 301.

The resistor 401 is an element that discharges the charge of the capacitor 400. The resistor 401 has one end connected to the ground side node of each of the light sources D0 to D9, and the other end connected to the drain electrode of the driving transistor 301. Therefore, the resistor 401 is connected in parallel to the capacitor 400. Note that the capacitor 400 corresponds to a "second capacitor".

==About the current waveform of the light emitting device 20c==
Here, the waveform of the current flowing through the light source of the light emitting device 20c will be explained. In this embodiment, the capacitance of the capacitor 400 is, for example, 2000 pF, and each of the capacitors 314 of the power supply circuits 70 to 79 uses a capacitor having a capacitance sufficiently larger than 2000 pF (for example, 0.1 μF).

However, the capacitors 314 of each of the power supply circuits 70 to 79 have variations. In this embodiment, the capacitance of the capacitor 314 of the power supply circuit 70 is, for example, 0.11 μF, the capacitance of the capacitor 314 of the power supply circuit 71 is, for example, 0.1 μF, and the capacitance of the capacitor 314 of the power supply circuit 72 is, for example, The explanation will be made assuming that it is 0.09 μF.

Further, currents I0 to I2 flowing through the light sources D0 to D2 will be explained here with reference to FIG. In addition, in FIG. 9, the current I0 is shown as a solid line, the current I1 is shown as a dotted line with wide intervals, and the current I2 is shown as a dotted line with narrow intervals. Although details will be described later, in this embodiment, the waveforms of the currents I0 to I2 are approximately the same, so the three current waveforms overlap in FIG. 9.

When the power supply circuit 70 in FIG. 8 is generating the power supply voltage V10 (that is, the signal S10 is at the H level), for example, when the signal S20 goes to the H level at time t30 in FIG. Turns on.

As a result, capacitor 314 of power supply circuit 70 is discharged, and the charging current for charging capacitor 400 increases. In this embodiment, the charging current of the capacitor 400 becomes the current I0 that lights up the light source D0, so the current I0 increases.

Thereafter, capacitor 400 is gradually charged, and when current I0 reaches a peak value, current I0 decreases. Then, since the discharged capacitor 314 is charged, the current I0 decreases to almost zero. Thereafter, the driving transistor 301 is turned off at a predetermined timing. Note that when the driving transistor 301 is turned off, the capacitor 400 is discharged via the resistor 401.

Here, we have explained the current I0 when the power supply circuit 70 is generating the power supply voltage V10, but as shown in FIG. The waveforms of the currents I1 and I2 also become the charging current of the capacitor 400. Therefore, as shown in FIG. 9, each of the currents I0 to I2 has substantially the same waveform.

In this way, in the light emitting device 20c, if the capacitance of the capacitor 314 included in the power supply circuits 70 to 79 is sufficiently larger than the capacitance of the capacitor 400, the waveform and peak value of the currents I0 to I9 are determined by the capacitance of the capacitor 400. become. Therefore, in the light emitting device 20c, even when the measurement distance is increased, variations in the currents I0 to I9 can be suppressed.

Note that when the measurement distance is relatively short, the capacitance of each of the plurality of capacitors 314 in the power supply circuits 70 to 79 in the light emitting device 20b in FIG. 4 can be reduced. In such a case, variations in the plurality of capacitors 314 of the power supply circuits 70 to 79 are generally reduced, and therefore variations in the intensity of light emitted from the light sources D0 to D9 are also reduced. Therefore, when the measurement distance is relatively short, the light emitting device 20b can be used.

===Other embodiments===
In this embodiment, a VCSEL is used for each of the light sources D0 to D9, but the present invention is not limited to this, and for example, a light emitting diode may be used. Even when light emitting diodes are used as the light sources D0 to D9, a light emitting device can be realized with a simple configuration, as in this embodiment.

===Summary===
The measuring device 10 of this embodiment has been described above. In the light emitting device 20b, a driving transistor 301 is provided between the ground side nodes of the light sources D0 to D9 and the ground. Therefore, when the driving transistor 301 is turned on while the power supply voltage is being supplied to the light source that is the target of light emission, the light source that is the target of light emission can be turned on. Therefore, the light emitting device 20b has a small number of parts and can light a plurality of light sources with a simple configuration.

Further, in the light emitting device 20b, for example, when the power supply circuit 70 is generating the power supply voltage V10, the power supply circuits 71 to 79 are discharging the capacitors 314 (not shown) inside each of them. Therefore, when the driving transistor 301 is turned on, only a desired light source among the plurality of light sources can be turned on. Furthermore, when the measurement distance is relatively short, variations in the capacitors 314 of the power supply circuits 71 to 79 are small. Therefore, in such a case, the light emitting device 20b can be used.

Further, in the power supply circuit 70 , a resistor 313 is provided between a push-pull circuit composed of a PMOS transistor 311 and an NMOS transistor 312 and a capacitor 314 . Therefore, the charging current and discharging current of the capacitor 314 can be limited to appropriate current values. Furthermore, the components that make up the power supply circuit 70 can use low-power components compared to the components that make up the power supply circuit 50.

Further, as shown in FIGS. 4 and 5, for example, the control circuit 80 controls the power supply circuit so that the capacitor 314 (not shown) of the power supply circuit 71 is charged when the capacitor 314 of the power supply circuit 70 is discharged. 70 and 71 are controlled. That is, in this embodiment, since the generation of the power supply voltage V11 is started before the power supply voltage V10 becomes 0V, the light source D1 can be turned on smoothly after the light source D0 is turned off.

Further, in the light emitting device 20c, a capacitor 400 and a resistor 401 are provided between the light sources D0 to D9 and the driving transistor 301. Therefore, in the light emitting device 20c, the charging current of the capacitor 400 becomes the currents I0 to I9, so that variations in the currents I0 to I9 can be suppressed.

Further, in the light emitting device 20c, the capacitance of each capacitor 314 of the power supply circuits 70 to 79 is larger than the capacitance of the capacitor 400. Therefore, capacitor 314 can supply sufficient current to capacitor 400.

Further, for example, in the light emitting device 20c, the capacitance of the capacitor 400 is, for example, 1000 pF or more. As a result, in the light emitting device 20c, the peak values of the currents I0 to I9 can be increased, so that the measurement distance can be extended.

Further, as the light source D0, a VCSEL can be used, but for example, like a VCSEL, a light emitting diode having a cathode and an anode may also be used. In such a case, the light source D0 will include a light emitting diode and an optical member 120.

The above-described embodiments are provided to facilitate understanding of the present invention, and are not intended to be interpreted as limiting the present invention. Further, the present invention can be modified and improved without departing from the spirit thereof, and it goes without saying that the present invention includes equivalents thereof.

10 Measuring device 11 Target object 20, 20a, 20b Light emitting device 21 Light receiving device 22 Control device 40, 201, 314, 400 Capacitor 41, 212 IC
50-59 Power supply circuit 60 Control circuit 100-115 Laser diode 120 Optical member 200 Diode 210, 230, 300, 310 Buffer 211 Transformer 213, 313, 401 Resistor 220 Primary coil 221 Secondary coil 231, 301 Drive transistor 312 NMOS Transistor 311 PMOS transistor D0 to D9 Light source

Claims (8)

n light sources (n≧2);
the n power supply circuits provided for each of the n light sources;
a switch provided between a ground side node of each of the n light sources and the ground;
Equipped with
The power supply circuit generates a power supply voltage for a corresponding one of the n light sources based on a first signal, and stops generating the power supply voltage based on a second signal,
The switch is turned on based on a turn-on instruction and turned off based on a turn-off instruction when the power supply voltage for the one light source is generated.
Light emitting device. The light emitting device according to claim 1,
The power supply circuit is
a first capacitor on which the power supply voltage is generated;
a charging/discharging circuit that charges the first capacitor based on the first signal and discharges the first capacitor based on the second signal;
A light-emitting device including. The light emitting device according to claim 2,
including a resistor provided between the charging/discharging circuit and the first capacitor;
Light emitting device. The light emitting device according to claim 3,
a control circuit that outputs the first and second signals to each of the n power supply circuits and controls each of the n power supply circuits;
The control circuit includes:
Among the n power supply circuits, the first and second power supply circuits are configured such that when the first capacitor of the first power supply circuit is being discharged, the first capacitor of the second power supply circuit is charged. control,
Light emitting device. The light emitting device according to claim 2,
a second capacitor provided between a ground side node of each of the n light sources and the switch;
a resistor connected in parallel to the second capacitor;
A light emitting device comprising: The light emitting device according to claim 5,
The capacitance of the first capacitor is larger than the capacitance of the second capacitor.
Light emitting device. 7. The light emitting device according to claim 6,
The capacitance of the second capacitor is 1000 pF or more,
Light emitting device. The light emitting device according to any one of claims 1 to 7,
The light source includes either a laser diode or a light emitting diode, and an optical member that adjusts the distribution of light from either of the elements.
Light emitting device.

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