Patent Application
20230078833
This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2021-146777 filed Sep. 9, 2021.
The present invention relates to a light emitting device and a detection apparatus.
JP2020-188239A describes that in a light emitting device, a general-purpose (normal) capacitor is further connected to a series circuit of a light emitting element and a transistor.
There is a technique for causing the light emitting element to emit light by supplying a current to the light emitting element by an electric accumulator that applies a voltage to a power supply and accumulates electric charge. Further, in a resonant circuit in which an electric accumulator is provided and which generates resonance, a current generated by the resonance may be supplied to the light emitting element. In such a case, in a configuration in which the circuit from the power supply to the resonant circuit is constantly conductive, the electric charge may be supplied from the power supply to the resonant circuit even in a case where the current in the resonant circuit is supplied to the light emitting element, and resonance in the resonant circuit may be attenuated.
Aspects of non-limiting embodiments of the present disclosure relate to a light emitting device and a detection apparatus that suppress attenuation of resonance in the resonant circuit as compared with a configuration in which the circuit from the power supply to the resonant circuit is being constantly conductive.
Aspects of certain non-limiting embodiments of the present disclosure overcome the above disadvantages and/or other disadvantages not described above. However, aspects of the non-limiting embodiments are not required to overcome the disadvantages described above, and aspects of the non-limiting embodiments of the present disclosure may not overcome any of the disadvantages described above.
According to an aspect of the present disclosure, there is provided a light emitting device including: a resonant circuit that is provided with an electric accumulator accumulating electric charge and generates resonance; a light emitting element that emits light in a case where a current in the resonant circuit is supplied; and a first switching unit that is connected to a circuit between a power supply that supplies electric charge to the electric accumulator and the resonant circuit, and switches between a conduction state in which a circuit from the power supply to the resonant circuit is conductive and a non-conduction state in which the circuit is not conductive.
Exemplary embodiment(s) of the present invention will be described in detail based on the following figures, wherein:
Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.
Further, in the LiDAR, the time of flight (TOF) is used. The TOF is to measure the distance to the target object T on the basis of a time period in which light travels. The TOF includes the indirect time of flight (iTOF) and the direct time of flight (dTOF). The iTOF is a method of measuring the distance to the target object T on the basis of a difference between a phase of the emitted light and a phase of the received light. Further, the dTOF is a method of measuring the distance to the target object T on the basis of a time period from emission of the light to light reception. The detection apparatus 1 of the present exemplary embodiment detects the distance to the target object T by the dTOF. However, the detection apparatus 1 may detect the distance to the target object T by the iTOF.
The detection apparatus 1 of the present exemplary embodiment includes a light emitting device 10, a light receiving unit 20, and a detection unit 30.
The light emitting device 10 is a device which emits light. Examples of the light emitting device 10 include a vertical cavity surface emitting laser (VCSEL). The VCSEL is a laser which emits light in a direction perpendicular to a surface of a substrate. Further, the light emitting device 10 of the present exemplary embodiment generates a current by resonance, and emits pulsed light by the generated current. The light emitting device 10 includes a light emitting element 11 and a substrate 12.
The light emitting element 11 is an element which emits light in a case where a current is supplied. The light emitting element 11 emits light in a direction perpendicular to a surface of the substrate 12.
The substrate 12 is a substrate on which a part of the resonant circuit is provided. A resonant circuit is an electronic circuit in which resonance occurs.
The light receiving unit 20 as an example of the light receiving unit receives light based on irradiation of the target object T with the light emitted from the light emitting device 10. Further, in a case where the light receiving unit 20 receives light, electric charge is generated. Examples of the light based on the irradiation of the target object T with the light emitted from the light emitting device 10 include light emitted from the light emitting device 10 and reflected by the target object T, and light scattered by irradiating the target object T with the light emitted from the light emitting device 10. The light emitted from the light emitting device 10 may be referred to as emitted light below. Further, the light emitted from the light emitting device 10 and reflected by the target object T is hereinafter referred to as reflected light. Further, the light scattered by irradiating the target object T with the light emitted from the light emitting device 10 is hereinafter referred to as scattered light.
Examples of the light receiving unit 20 include an optical sensor which detects light. Further, examples of the optical sensor include semiconductors such as a single photon avalanche diode (SPAD).
The detection unit 30 as an example of the detection unit detects the distance from the detection apparatus 1 to the target object T, on the basis of the light received by the light receiving unit 20. The detection unit 30 has a time measurement unit 31 and a measurement unit 32.
The time measurement unit 31 measures a time period. The measurement unit 32 acquires information indicating the time period from the light emission from the light emitting device 10 to the generation of electric charge from the light receiving unit 20 from the time measurement unit 31. Then, from the acquired information, the distance from the detection apparatus 1 to the target object T is measured. More specifically, the measurement unit 32 measures the distance from the detection apparatus 1 to the target object T from Expression (1).
L=(c×t)/2 (1)
In Expression (1), L is the distance from the detection apparatus 1 to the target object T. Further, c is a speed of light. Further, t is a time period from emission of light from the light emitting device 10 to generation of electric charge by the light receiving unit 20. In addition, the measurement unit 32 measures the distance from the detection apparatus 1 to the target object T by setting a time period from emission of light from the light emitting device 10 to generation of electric charge by the light receiving unit 20 to a time period from when emission of light from the light emitting device 10 to light reception of the light receiving unit 20.
The detection apparatus 1 is provided in a movable body 2 which is traveling. In the illustrated example, an automobile is shown as the movable body 2. The movable body 2 is not limited to the illustrated example. The movable body 2 may be, for example, a drone, a train, a ship, an airplane, or the like. Further, the movable body 2 may be a computer carried by the user of the detection apparatus 1.
Further, in the illustrated example, a human being is shown as the target object T, but the target object T is not limited to the human being. The target object T may be any object as long as the object reflects the light emitted from the light emitting device 10 or scatters the light by being irradiated with the light emitted from the light emitting device 10.
Further, the detection apparatus 1 of the present exemplary embodiment sets the distance to the target object T as a detection target from a plurality of stages. Then, the detection apparatus 1 includes a distance of 10 m as the distance to the target object T as a detection target.
Next, a configuration of the light emitting device 10 will be described.
As shown in
Further, the light emitting device 10 is provided with a power supply 13, a capacitor 14, an operation unit 15, a switching unit 16, and a control unit 17.
The power supply 13 supplies electric charge to the capacitor 14.
The capacitor 14 as an example of the electric accumulator is an element which accumulates electric charge. Further, the capacitor 14 supplies a current to the light emitting element 11 by discharging the accumulated electric charge. The capacitor 14 may be provided as a part of a plurality of layers constituting the substrate 12, or may be provided as a component which is separate from the substrate 12. In the present exemplary embodiment, a capacitance of the capacitor 14 is determined such that a current necessary for the light emitting element 11 to emit light once is accumulated in the capacitor 14.
The operation unit 15 is an integrated circuit (IC) which operates the light emitting element 11. The operation unit 15 is provided with a transistor 151.
The transistor 151 as an example of a second switching unit is an electronic switch which switches between a state in which the resonant circuit RC is conductive and a state in which the resonant circuit RC is not conductive, depending on the applied voltage. In a case where a voltage equal to or greater than a predetermined value is not applied to the transistor 151, the transistor 151 is in an OFF state. In such a case, since a circuit to which the transistor 151 is connected is cutoff and the resonant circuit RC is being not conductive, no current is supplied to the light emitting element 11. Further, in a case where a voltage equal to or greater than a predetermined value is applied to the transistor 151, the transistor 151 is in an ON state. In such a case, since the circuit to which the transistor 151 is connected is connected and the resonant circuit RC is in a conduction state, the circuit is in a resonance state in the resonant circuit and the generated current is supplied to the light emitting element 11. In the present exemplary embodiment, an application unit (not shown) for applying a voltage to the transistor 151 is provided in the operation unit 15, and the application unit controls the transistor 151 to switch the transistor 151 into either one of an ON state and an OFF state.
Further, in the following, a state in which the transistor 151 conducts the resonant circuit RC may be referred to as a conduction state. Further, a state in which the transistor 151 does not conduct the resonant circuit RC may be referred to as a non-conduction state. The conduction state of the transistor 151 is a state in which the transistor 151 is ON. Further, the non-conduction state of the transistor 151 is a state in which the transistor 151 is OFF.
The switching unit 16 as an example of the first switching unit is a switch which switches between a state in which a circuit from the power supply 13 to the resonant circuit RC is conductive and a state in which the circuit is not conductive. In the present exemplary embodiment, a transistor is used as the switching unit 16. The switching unit 16 is connected to the circuit between the power supply 13 and the resonant circuit RC. Then, the switching unit 16 switches between a state in which the circuit from the power supply 13 to the resonant circuit RC is conductive and a state in which the circuit is not conductive, depending on the applied voltage.
In a case where a voltage equal to or greater than a predetermined value is applied to the switching unit 16, the switching unit 16 is in an ON state. In such a case, the circuit to which the switching unit 16 is connected is connected, and the circuit from the power supply 13 to the resonant circuit RC is in a conduction state. Therefore, the capacitor 14 is charged by supplying the electric charge from the power supply 13 to the capacitor 14.
Further, in a case where a voltage equal to or greater than a predetermined value is not applied to the switching unit 16, the switching unit 16 is in an OFF state. In such a case, the circuit to which the switching unit 16 is connected is cutoff, and the circuit from the power supply 13 to the resonant circuit RC is being not conductive. At this time, no electric charge is supplied from the power supply 13 to the capacitor 14.
In the following, a state in which the switching unit 16 conducts a circuit from the power supply 13 to the resonant circuit RC may be referred to as a conduction state. Further, a state in which the switching unit 16 does not conduct the circuit from the power supply 13 to the resonant circuit RC may be referred to as a non-conduction state. The conduction state of the switching unit 16 is a state in which the switching unit 16 is ON. Further, the non-conduction state of the switching unit 16 is a state in which the switching unit 16 is OFF.
The control unit 17 as an example of the switching control unit switches between the conduction state and the non-conduction state of the switching unit 16. More specifically, the control unit 17 switches between a conduction state and a non-conduction state of the switching unit 16 by switching whether or not to apply a voltage equal to or greater than a predetermined value to the switching unit 16. As the control unit 17, for example, a gate driver is used.
In the present exemplary embodiment, in a case where the transistor 151 is in the non-conduction state and the switching unit 16 is in the conduction state, the resonant circuit RC is being not conductive, while the circuit from the power supply 13 to the capacitor 14 is being conductive. In such a case, electric charge is supplied from the power supply 13 to the capacitor 14, and the capacitor 14 is charged.
Further, in a case where the transistor 151 is in a conduction state and the switching unit 16 is in a non-conduction state, the resonant circuit RC is being conductive, while the circuit from the power supply 13 to the capacitor 14 is being not conductive. In such a case, the light emitting element 11 emits light by supplying a current from the capacitor 14 to the light emitting element 11. Further, after the current is supplied from the capacitor 14 to the light emitting element 11, the transistor 151 is put into the non-conduction state and the switching unit 16 is put into the conduction state again, and the capacitor 14 is charged. As described above, in the present exemplary embodiment, charging of the capacitor 14 and light emission of the light emitting element 11 by supplying a current from the capacitor 14 to the light emitting element 11 are repeatedly performed. Thereby, the light emitting element 11 intermittently emits pulsed light.
As described above, in the present exemplary embodiment, the switching unit 16 is connected to the circuit between the power supply 13 and the resonant circuit RC. Then, the switching unit 16 switches between a conduction state in which the circuit from the power supply 13 to the resonant circuit RC is conductive and a non-conduction state in which the circuit is not conductive.
Here, a method of causing the light emitting element 11 to emit light by supplying a current generated by resonance to the light emitting element 11 with a configuration different from the configuration of the present exemplary embodiment is also conceivable. For example, there is a configuration in which the light emitting element 11 is made to emit light by supplying the light emitting element 11 with the current generated by resonance, in a state where the circuit from the power supply 13 to the resonant circuit RC is constantly conductive, without providing the switching unit 16 in the circuit between the power supply 13 and the resonant circuit RC. However, according to such a configuration, electric charge may be supplied from the power supply 13 to the capacitor 14 even in a case where resonance is being generated. As described above, in a case where the resonant circuit RC is affected by the circuit outside the resonant circuit RC while the resonance is being generated, the resonance in the resonant circuit RC may be attenuated.
Therefore, in the present exemplary embodiment, attenuation of resonance in the resonant circuit RC is suppressed by using a configuration of switching between a state in which the circuit from the power supply 13 to the resonant circuit RC is conductive and a state in which the circuit is not conductive, compared with the configuration in which the circuit from the power supply 13 to the resonant circuit RC is constantly conductive.
First, at the time point T1, the transistor 151 is in the non-conduction state, and the switching unit 16 is in the non-conduction state. At the time point T1, it is assumed that the charging of the capacitor 14 is completed. At this time, the capacitor 14 does not supply a current to the light emitting element 11, and the power supply 13 does not supply electric charge to the capacitor 14.
Next, at the time point T2, the transistor 151 switches from the non-conduction state to the conduction state. On the other hand, the switching unit 16 is in a non-conduction state. In such a case, the light emitting element 11 emits light in a case where the capacitor 14 supplies a current to the light emitting element 11. At this time, the current supplied from the capacitor 14 to the light emitting element 11 is the current generated by resonance in the resonant circuit RC. Further, the power supply 13 does not supply electric charge to the capacitor 14.
Then, at the time point T3, the transistor 151 switches from the conduction state to the non-conduction state. Further, at this time, the switching unit 16 is in a non-conduction state. In such a case, the capacitor 14 does not supply a current to the light emitting element 11, and the power supply 13 does not supply electric charge to the capacitor 14.
Then, at the time point T4, the control unit 17 turns on the switching unit 16. Therefore, the switching unit 16 switches from the non-conduction state to the conduction state. Further, at this time, the transistor 151 is in a non-conduction state. In such a case, the power supply 13 supplies electric charge to the capacitor 14, and the capacitor 14 is charged.
Then, charging of the capacitor 14 is completed.
Then, at the time point T5, the control unit 17 turns off the switching unit 16. Therefore, the switching unit 16 switches from the conduction state to the non-conduction state. At this time, the transistor 151 is in a non-conduction state. In such a case, the capacitor 14 does not supply a current to the light emitting element 11, and the power supply 13 does not supply electric charge to the capacitor 14.
Then, at the time point T6, the transistor 151 switches from the non-conduction state to the conduction state. At this time, the switching unit 16 is in a non-conduction state. In such a case, the capacitor 14 supplies a current to the light emitting element 11. Therefore, the light emitting element 11 re-emits light. On the other hand, the power supply 13 does not supply electric charge to the capacitor 14.
Then, at the time point T7, the transistor 151 switches from the conduction state to the non-conduction state. At this time, the switching unit 16 is in a non-conduction state. In such a case, the capacitor 14 does not supply a current to the light emitting element 11, and the power supply 13 does not supply electric charge to the capacitor 14.
Then, at the time point T8, the control unit 17 turns on the switching unit 16. Therefore, the switching unit 16 switches from the non-conduction state to the conduction state. At this time, the transistor 151 is in a non-conduction state. In such a case, the power supply 13 supplies electric charge to the capacitor 14, and the capacitor 14 is charged again.
In the present exemplary embodiment, a timing at which the transistor 151 is turned on is determined on the basis of a timing at which the charging of the capacitor 14 is completed. More specifically, the timing at which the transistor 151 is turned on is determined such that the transistor 151 switches from the non-conduction state to the conduction state after the charging of the capacitor 14 is completed.
Further, a timing at which the transistor 151 is turned off is determined on the basis of a timing at which there is no electric charge to be accumulated in the capacitor 14. More specifically, the timing at which the transistor 151 is turned off is determined such that the transistor 151 switches from the conduction state to the non-conduction state after there is no electric charge to be accumulated in the capacitor 14 by causing the capacitor 14 to supply the current necessary for one light emission of the light emitting element 11.
Further, in the present exemplary embodiment, as described above, the detection apparatus 1 sets the distance to the target object T as a detection target from a plurality of stages. Then, the time period t1 from switching of the transistor 151 to the non-conduction state to switching of the transistor 151 to the conduction state is determined in accordance with a distance which is set in the detection apparatus 1 as the detection target. It is determined that the time period t1 is longer as the distance which is set in the detection apparatus 1 as the detection target is longer. Here, the time period t1 is also taken as a time interval from light emission of the light emitting element 11 to re-emission of the light emitting element 11.
Further, a timing at which the control unit 17 puts the switching unit 16 into an ON state is determined on the basis of a timing at which the transistor 151 is OFF. More specifically, a timing at which the control unit 17 puts the switching unit 16 into an ON state is determined such that the switching unit 16 switches from the non-conduction state to the conduction state in a case where the time period t2 elapses after the transistor 151 is switched to the non-conduction state.
Further, a timing at which the control unit 17 puts the switching unit 16 into an OFF state is determined on the basis of a timing at which the transistor 151 is turned ON. More specifically, a timing at which the control unit 17 turns off the switching unit 16 is determined such that the switching unit 16 switches from the conduction state to the non-conduction state at a time which is earlier by the time period t3 than a time at which the transistor 151 switches from the non-conduction state to the conduction state.
In the present exemplary embodiment, a timing at which the control unit 17 applies the voltage to the switching unit 16 is set in advance in the control unit 17. Therefore, the timing at which the switching unit 16 is turned on and the timing at which the switching unit 16 is turned off are determined. Further, by setting the timing at which the voltage is applied to the transistor 151 to the operation unit 15 in advance, the timing at which the transistor 151 is turned on and the timing at which the transistor 151 is turned off are determined. A user of the detection apparatus 1 performs both setting of the timing at which the control unit 17 applies the voltage to the switching unit 16 and setting of the timing at which the voltage is applied to the transistor 151.
As described above, in the present exemplary embodiment, the switching unit 16 is in a non-conduction state in a case where the capacitor 14 supplies the current to the light emitting element 11.
In particular, in the present exemplary embodiment, in a case where the switching unit 16 is in the conduction state and the transistor 151 is in the non-conduction state, the control unit 17 puts the switching unit 16 into the non-conduction state before the transistor 151 switches to the conduction state.
Further, in the present exemplary embodiment, the switching unit 16 is in a conduction state in a case where the capacitor 14 does not supply a current to the light emitting element 11.
In particular, in the present exemplary embodiment, in a case where the switching unit 16 is in the non-conduction state and the transistor 151 is in the conduction state, the control unit 17 puts the switching unit 16 into the conduction state after the transistor 151 is switched to the non-conduction state.
Further, in the present exemplary embodiment, the time at which the transistor 151 is conductive and the time at which the transistor 151 is non-conduction state are predetermined. Then, the time, at which the control unit 17 puts the switching unit 16 into the non-conduction state, is determined in accordance with a time at which the transistor 151 becomes the conduction state, and the time, at which the control unit 17 puts the switching unit 16 into the conduction state, is determined in accordance with a time at which the transistor 151 becomes the non-conduction state.
Further, in the present exemplary embodiment, the time period from the non-conduction state of the transistor 151 to the conduction state is determined in accordance with the distance to the target object T which is set in the detection apparatus 1 as the detection target. More specifically, it is defined that the longer the distance to the target object T included in the detection apparatus 1 as the detection target, the longer the time period from the non-conduction state to the conduction state of the transistor 151.
Even in a case where the distance to the target object T which is set in the detection apparatus 1 as the detection target is long, a time interval between the end of the light emission and the light re-emission of the light emitting element 11 may be short. In such a case, the light emitting element 11 may emit light a plurality of times until the light receiving unit 20 receives the light once. In such a case, it is difficult for the detection unit 30 to identify which of the light received by the light receiving unit 20 is based on the light emitted from the light emitting element 11 at which timing. Therefore, in the present exemplary embodiment, the time period from the non-conduction state to the conduction state of the transistor 151 is determined in accordance with the distance to the target object T which is set in the detection apparatus 1 as the detection target.
First, the transistor 151 of the operation unit 15 becomes the conduction state (step (hereinafter referred to as “S”) 1). At this time, it is assumed that charging of the capacitor 14 is completed and the switching unit 16 is in a non-conduction state.
The capacitor 14 supplies a current to the light emitting element 11 (S2).
The light emitting element 11 emits light in a case where a current is supplied from the capacitor 14 (S3).
The transistor 151 becomes a non-conduction state (S4). The control unit 17 turns on the switching unit 16 (S5). Thereby, the switching unit 16 becomes conduction state (S6).
The power supply 13 supplies electric charge to the capacitor 14 (S7). Thereby, the capacitor 14 is charged.
The control unit 17 puts the switching unit 16 into an OFF state (S8). Thereby, the switching unit 16 is in a non-conduction state (S9).
Then, the light receiving unit 20 receives light (S10). More specifically, the light receiving unit 20 receives the light generated by irradiating the target object T with the light emitted from the light emitting element 11 in step S3.
The detection unit 30 detects the distance to the target object T on the basis of the light received by the light receiving unit 20 (S11).
Then, the transistor 151 becomes the conduction state again (S12).
The capacitor 14 supplies a current to the light emitting element 11 (S13).
The light emitting element 11 re-emits light in a case where the current in the resonant circuit RC is supplied from the capacitor 14 (S14).
Then, each time period the current is supplied from the capacitor 14 to the light emitting element 11, the capacitor 14 is charged, the light receiving unit 20 receives the light, and the detection apparatus 1 detects the distance to the target object T.
Then, in a case where the final light emission of the plurality of light emissions by the light emitting element 11 is performed, the transistor 151 is put into a non-conduction state (S15).
The control unit 17 puts the switching unit 16 (S16) into an ON state. Thereby, the switching unit 16 becomes the conduction state (S17).
The power supply 13 supplies electric charge to the capacitor 14 (S18). Thereby, the capacitor 14 is charged.
The control unit 17 puts the switching unit 16 into an OFF state (S19). Thereby, the switching unit 16 is in a non-conduction state (S20).
Then, the light receiving unit 20 receives the light (S21).
The detection unit 30 detects the distance to the target object T on the basis of the light received by the light receiving unit 20 (S22).
Here, as shown in
In the present exemplary embodiment, it is assumed that an inductance in the resonant circuit RC is 0.4 nH and a capacitance of the capacitor 14 is 200 pF. Further, it is assumed that an electric resistance in the electric path from the power supply 13 to the resonant circuit RC is 10Ω. Further, it is assumed that the distance to the target object T which is set as a detection target by the detection apparatus 1 is 10 m.
The light emitting element 11 of the present exemplary embodiment emits light in a case where a current generated by resonance is supplied. In such a case, Relational Expression (2) is established between the resonant circuit RC and the light emitted from the light emitting element 11.
In Expression (2), f is the resonance frequency of the light emitted from the light emitting element 11. The resonance frequency of light is the frequency of light emitted from the light emitting element 11 in a case where resonance is being generated. Further, L is the inductance in the resonant circuit RC. Further, C is the capacitance of the capacitor 14.
Substituting the inductance L of the resonant circuit RC and the capacitance C of the capacitor 14 into Expression (2), f≈15.63×108 is calculated as the resonance frequency f.
Next, a method of calculating the time period from the start of emission of the light from the light emitting device 10 to the emission of the light having the maximum intensity will be described. In addition, in the present exemplary embodiment, it is assumed that reflected light is generated in a case where the target object T is irradiated with the light which is emitted from the light emitting device 10 and has the maximum intensity. Therefore, first, a time period from the start of emission of the light from the light emitting device 10 to the emission of the light having the maximum intensity is calculated.
An intensity of the light emitted from the light emitting element 11 changes into a wave shape with the passage of time. Specifically, at a timing in a case where the emission of the light from the light emitting element 11 is started, the intensity of the emitted light is a reference, and then the intensity of the emitted light is maximized. Subsequently, the intensity of the emitted light returns to the reference, and then the intensity of the emitted light is minimized. Further, then, the intensity of the emitted light returns to the reference again. In such a manner, the intensity of the light emitted from the light emitting element 11 changes periodically. Further, regarding the intensity of the light emitted from the light emitting element 11, the time period from the reference to the maximum, the time period from the maximum to the reference, the time period from the reference to the minimum, and the time period from the minimum to the reference again are all the same time period. Therefore, the time period Tc from the start of emission of the light from the light emitting device 10 to the emission of the light having the maximum intensity is calculated from Expression (3).
T
c
=T
p/4 (3)
In Expression (3), Tp is a period of oscillation in the emitted light. The period Tp is calculated from Expression (4).
T
p=1/f (4)
By substituting the resonance frequency f into Expression (4), Tp≈1.78×10−9 is calculated as the period Tp. Further, by substituting the period Tp into Expression (3), Tc=4.45×10−10 seconds is calculated as the time period Tc.
Next, a method of calculating the time period from emission of the light having the maximum intensity from the light emitting device 10 to light reception of the light receiving unit 20 will be described. The time period Tr from emission of the light from the light emitting device 10 to light reception of the light receiving unit 20 is calculated from Expression (5).
T
r=2Lt/c (5)
In Expression (5), Lt is the distance from the detection apparatus 1 to the target object T. Further, c is a speed of the light. By substituting the distance Lt and the speed c into Expression (5), Tr≈66.7×10−9 seconds is calculated as the time period Tr.
Next, a method of calculating the time period from the start of emission of the light from the light emitting device 10 to light reception of the light receiving unit 20 will be described. Since the time period Ts from the start of emission of the light from the light emitting device 10 to the reception by the light receiving unit 20 is the sum of the time period Tc and the time period Tr, Ts≈67.1×10−9 seconds is calculated as the time period Ts.
Next, a method of calculating the time period necessary to charge the capacitor 14 will be described. The relationship of Expression (6) is established in the time period in which the capacitor 14 is charged, the electric resistance, and the capacitance C of the capacitor 14.
T
t
=RC (6)
In Expression (6), Tt is a time constant for charging the capacitor 14, and R is an electric resistance of the electric path from the power supply 13 to the resonant circuit RC. The time constant Tt is the time period necessary for the capacitor 14 to be charged to 63% of the capacity thereof. By substituting the electric resistance R and the capacitance C into Expression (6), Tt=2×10−9 seconds is calculated as the time constant Tt.
Next, a method of calculating the time period from the start of charging of the capacitor 14 to the completion of charging will be described. In a case where a time period five times the time constant Tt elapses from the start of charging of the capacitor 14, the capacitor 14 is charged to 99.3% of the capacity thereof. That is, in a case where a time period five times the time constant Tt elapses after the charging of the capacitor 14 is started, the charging of the capacitor 14 is completed. Therefore, Tz=5×Tt=10×10−9 seconds is calculated as the time period Tz from the start of charging of the capacitor 14 to the completion of charging.
As described above, the time period Ts from the start of emission of the light from the light emitting device 10 to the light reception by the light receiving unit 20 is 67.1×10−9 seconds. In contrast, the time period Tz from the start of the charging of the capacitor 14 to the completion of charging is 10×10−9 seconds. That is, in the present exemplary embodiment, the charging of the capacitor 14 is completed from light emission of the light emitting device 10 to light reception of the light receiving unit 20.
In the present exemplary embodiment, it has been described that the electric resistance of the electric path from the power supply 13 to the resonant circuit RC in a case where the switching unit 16 is in a conduction state is 100, but the present invention is not limited to this.
For example, it is assumed that the electric resistance of the electric path from the power supply 13 to the resonant circuit RC is 500 in a case where the switching unit 16 is in a conduction state. In such a case, Tt=10×10−9 seconds is calculated as the time constant Tt. Further, the time period Tz from the start of charging of the capacitor 14 to the completion of charging is calculated as Tz=5×Tt=50×10−9 seconds. Even in such a case, the charging of the capacitor 14 is completed from light emission of the light emitting device 10 emits light to light reception of the light receiving unit 20. That is, in order to complete the charging of the capacitor 14 from light emission of the light emitting device 10 to light reception of the light receiving unit 20, an electric resistance of the electric path from the power supply 13 to the resonant circuit RC in a case where the switching unit 16 is in a conduction state may be 500 or less.
As described above, in the present exemplary embodiment, the electric charge necessary to supply the current for light emission of the light emitting element 11 is accumulated in the capacitor 14 from supply of the current necessary for light emission of the light emitting element 11 from the capacitor 14 to light reception of the light receiving unit 20 on the basis of the light emission.
In the comparative example, the resistor 18 is connected to the electric path between the power supply 13 and the resonant circuit RC. Then, the resistor 18 suppresses the supply of electric charge from the power supply 13 to the capacitor 14, thereby suppressing the attenuation of resonance in the resonant circuit RC.
The resistor 18 has a predetermined electric resistance. In the comparative example, the resistor 18 is used, which has an electric resistance determined such that the electric resistance in the electric path from the power supply 13 to the resonant circuit RC is the lower limit value of the electric resistance necessary for attenuation of the resonance in the resonant circuit RC. The lower limit value of the electric resistance necessary for the attenuation of resonance in the resonant circuit RC may be referred to as an electric resistance R1 below. The electric resistance R1 is an example of the first electric resistance. Further, the electric resistance of the electric path from the power supply 13 to the resonant circuit RC in the light emitting device 10 of the present exemplary embodiment may be referred to as an electric resistance R2 below. The electric resistance R2 is an example of the second electric resistance.
Even with the configuration shown in
Therefore, in the present exemplary embodiment, the switching unit 16 is provided in the circuit between the power supply 13 and the capacitor 14 without providing a resistor. In such a configuration, the electric resistance of the electric path from the power supply 13 to the resonant circuit RC in a case where the switching unit 16 is in a conduction state is smaller than the electric resistance R1. In such a case, as compared with the comparative example, as it is easier to supply the electric charge from the power supply 13 to the capacitor 14, the time period necessary to charge the capacitor 14 is shorter.
In the light emitting device 10 in the comparative example, as shown in
Then, at the time point T12, there is no electric charge to be accumulated in the capacitor 14. Further, at this time, the transistor 151 is put into a non-conduction state, and the light emitting element 11 is turned off.
Then, at the time point T13, supply of electric charge from the power supply 13 to the capacitor 14 is started, and charging of the capacitor 14 is started.
Then, at the time point T14, a necessary amount of electric charge is supplied from the power supply 13 to the capacitor 14. Thereby, the charging of the capacitor 14 is completed. The necessary amount of electric charge is the amount of electric charge necessary to be accumulated in the capacitor 14 in order for the light emitting element 11 to emit light by causing the capacitor 14 to supply a current to the light emitting element 11. The necessary amount of electric charge is an example of the first amount of electric charge.
Then, at the time point T15, the transistor 151 becomes the conduction state, and the supply of current from the capacitor 14 to the light emitting element 11 is restarted. Thereby, the light emission of the light emitting element 11 is restarted.
In the comparative example, the time period from the start to the completion of charging of the capacitor 14 is the time period t10 from the time point T13 to the time point T14. The time period from start of the charging of the capacitor 14 is started to light emission of the light emitting element 11 is a time period t11 from the time point T13 to the time point T15.
Further, in the light emitting device 10 of the present exemplary embodiment, as shown in
Then, at the time point T22, there is no electric charge to be accumulated in the capacitor 14. Further, at this time, the transistor 151 is put into a non-conduction state, and the light emitting element 11 is turned off.
Then, at the time point T23, the switching unit 16 becomes the conduction state, the supply of electric charge from the power supply 13 to the capacitor 14 is started, and the charging of the capacitor 14 is started.
Then, at the time point T24, the necessary amount of electric charge is supplied from the power supply 13 to the capacitor 14. Thereby, the charging of the capacitor 14 is completed. Then, the switching unit 16 becomes the non-conduction state.
Then, at the time point T25, the transistor 151 becomes the conduction state, and the supply of current from the capacitor 14 to the light emitting element 11 is restarted. Thereby, the light emission of the light emitting element 11 is restarted.
Then, at the time point T26, there is no electric charge to be accumulated in the capacitor 14 again. Further, at this time, the transistor 151 is put into a non-conduction state, and the light emitting element 11 is turned off.
Then, at the time point T27, the switching unit 16 becomes the conduction state, the supply of electric charge from the power supply 13 to the capacitor 14 is started, and the charging of the capacitor 14 is started again.
Then, at the time point T28, the necessary amount of electric charge is supplied from the power supply 13 to the capacitor 14. Thereby, the charging of the capacitor 14 is completed. Then, the switching unit 16 becomes the non-conduction state.
Then, at the time point T29, the transistor 151 becomes the conduction state, and the supply of current from the capacitor 14 to the light emitting element 11 is restarted. Thereby, the light emission of the light emitting element 11 is restarted.
In the present exemplary embodiment, the time period from the start to the completion of charging of the capacitor 14 is the time period t12 from the time point T23 to the time point T24. The time period from start of the charging of the capacitor 14 is started to light emission of the light emitting element 11 emits light is a time period t13 from the time point T23 to the time point T25. The time period from the end of light emission of the light emitting element 11 to the light re-emission of the light emitting element 11 is the time period t14 from the time point T22 to the time point T25.
Here, the time period t12 is shorter than the time period t10. Also, the time period t13 is shorter than the time period t10. Furthermore, the time period t14 is shorter than the time period t10.
That is, in the present exemplary embodiment, in a case where the electric resistance of the electric path from the power supply 13 to the resonant circuit RC is the electric resistance R1, the time period necessary to supply the necessary amount of electric charge from the power supply 13 to the capacitor 14 is the time period t10. In a case where the electric resistance of the electric path from the power supply 13 to the resonant circuit RC is the electric resistance R2, the time period from the end of light emission of the light emitting element 11 to the light re-emission of the light emitting element 11 is the time period t14 shorter than the time period t10.
In the present exemplary embodiment, it has been described that the circuit between the power supply 13 and the capacitor 14 is not provided with a resistor, but the present invention is not limited to this.
In a case where the electric resistance of the electric path from the power supply 13 to the resonant circuit RC in a case where the switching unit 16 is in a conduction state is smaller than the electric resistance R1, a resistor may be provided in the circuit between the power supply 13 and the capacitor 14.
Further, in the present exemplary embodiment, it has been described that in a case where the capacitor 14 supplies a current to the light emitting element 11, the switching unit 16 is constantly in a non-conduction state, but the present invention is not limited to this.
In a case where the switching unit 16 is constantly in a non-conduction state in a case where the capacitor 14 supplies a current to the light emitting element 11, the switching unit 16 may be in a conduction state in a case where the capacitor 14 supplies a current to the light emitting element 11. Even in such a case, attenuation of resonance in the resonant circuit RC is suppressed as compared with the configuration in which the circuit from the power supply 13 to the resonant circuit RC is being constantly conductive.
Although the exemplary embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the scope described in the above exemplary embodiments. It is clear from the description of the claims that the above-mentioned exemplary embodiment with various modifications or improvements is also included in the technical scope of the present invention.
The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-146777 | Sep 2021 | JP | national |
