Receiving device

Abstract

To provide a receiving device that can control, with a simple configuration, a reverse bias voltage applied to an APD during measurement.SOLUTION: A receiving device irradiates an object with an electromagnetic wave using a scanning mirror and measures a distance to the object on the basis of a reflected magnetic wave reflected on the object, and the receiving device has: an APD; an observation unit that observes output from the APD; and a control unit that, in a non-measurement period during which the distance is not measured occurring in a measurement period during which the distance is measured, increases a reverse bias voltage applied to the APD until the observed output from the APD reaches a predetermined amount, and controls the reverse bias voltage so that a multiplication factor of the APD becomes a predetermined value by using information acquired when the output from the APD reaches the predetermined amount.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a receiver that controls the operating voltage of a light receiving element having a multiplication effect. [Background technology]

[0002] APDs (Avalance Photodiodes) with a multiplication function are widely used as light receiving elements in LiDAR (Light Detection and Ranging), which is a distance measuring device that uses light. The multiplication factor of an APD is determined by the reverse bias voltage applied to the APD, but its multiplication factor characteristics (relationship between multiplication factor and reverse bias voltage) change with temperature. In addition, since the multiplication factor characteristics differ for each individual APD, in order to use it at the desired multiplication factor, it is necessary to appropriately control the reverse bias voltage according to the operating environment.

[0003] Patent Document 1 discloses a configuration in which the reverse bias voltage applied to the APD is adjusted to a voltage obtained by multiplying the reverse bias voltage when a predetermined current flows through the APD by a predetermined ratio.

[0004] Furthermore, Patent Document 2 discloses a configuration in which a light-shielding portion is used to reduce the amount of light entering the APD, a breakdown voltage is estimated from the APD output, and a reverse bias voltage that provides a desired multiplication factor, calculated based on the breakdown voltage, is applied to the APD. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2002-324909 A [Patent Document 2] JP 2022-163303 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the configuration of Patent Document 1, the reverse bias voltage when a predetermined current flows is detected during non-measurement, such as after the device is turned on or before measurement begins, and the multiplication factor cannot be controlled during measurement. Also, if light is incident on the APD when the reverse bias voltage is being detected, the current caused by the incident light may be amplified by the APD, causing an error in the detection of the reverse bias voltage, and it may not be possible to control the APD to a desired multiplication factor.

[0007] Furthermore, in the configuration of Patent Document 2, the provision of a light blocking portion makes the configuration complicated and reduces the range in which distance measurement is possible.

[0008] An object of the present invention is to provide a receiving device that is simply configured and capable of controlling the reverse bias voltage applied to an APD during measurement. [Means for solving the problem]

[0009] A receiving device according to one aspect of the present invention is a receiving device that irradiates an electromagnetic wave onto an object using a scanning mirror and measures the distance to the object based on the electromagnetic wave reflected by the object, and is characterized by having an APD, an observation unit that observes the output of the APD, and a control unit that increases a reverse bias voltage applied to the APD until the observed output of the APD reaches a predetermined amount during a non-measurement period in which the distance is not measured that occurs during a measurement period in which the distance is measured, and controls the reverse bias voltage so that the multiplication factor of the APD becomes a predetermined value using information obtained when the output of the APD reaches the predetermined amount. Effect of the Invention

[0010] According to the present invention, it is possible to provide a light receiving device that is capable of controlling the reverse bias voltage applied to an APD during measurement with a simple configuration. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing an overview of the configuration of a LiDAR according to an embodiment of the present invention. [Diagram 2]FIG. 1 is a diagram showing an overview of a configuration related to multiplication factor control of a LiDAR. [Diagram 3] FIG. 1 is a diagram showing an example of the temperature dependence of the multiplication factor characteristics of an APD. [Figure 4] FIG. 13 is a graph showing the gain characteristics of an APD when the reverse bias voltage is normalized by a reverse bias voltage near the breakdown voltage. [Diagram 5] 1 is a diagram illustrating a reception signal that causes the output of the APD to reach a predetermined amount when the amount of light incident on the APD is small. [Figure 6] 1 is a diagram illustrating a reception signal in which the output of the APD reaches a predetermined amount when the amount of light incident on the APD is large. [Figure 7] 1 is a diagram showing the relationship between the amount of light incident on the APD and the dispersion of the output of the APD 100. FIG. [Figure 8] 13 is a graph showing the relationship between the amount of light incident on an APD and the multiplication factor for a given amount A. FIG. [Figure 9] FIG. 4 is a diagram illustrating a scanning trajectory of a scanning mirror. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to refer to the same components, and duplicated descriptions will be omitted.

[0013] FIG. 1 is a diagram showing an outline of the configuration of a LiDAR according to an embodiment of the present invention. The LiDAR includes an APD (Avalance Photodiode) 100, an observation unit 200, an estimation unit 300, a control unit 400, and a scanning mirror 500. The LiDAR also includes a light source, a first optical system, a second optical system, and a detection and ranging unit. In the LiDAR, an electromagnetic wave emitted from a light source and guided to the scanning mirror 500 via the first optical system is irradiated onto an object by the scanning mirror 500. Here, the electromagnetic wave is, for example, a pulsed light emitted from a laser light source. Then, based on the reflected electromagnetic wave reflected by the object and guided to the detection and ranging unit via the second optical system, the detection and ranging unit measures the distance to the object. The observation unit 200 observes the output of the APD 100. The estimation unit 300 estimates (acquires) the amount of light incident on the APD 100 and the reverse bias voltage that provides a desired multiplication factor from the result of the observation unit 200. The control unit 400 controls the reverse bias voltage to be applied to the APD 100 based on the result of the estimation unit 300.

[0014] FIG. 2 is a diagram showing an overview of the configuration related to the multiplication factor control of the LiDAR. When light is incident on the APD100, photoelectric conversion occurs and a current flows. For the same amount of incident light, the higher the multiplication factor of the APD100, the higher the current flowing through the APD100. The multiplication factor varies according to the reverse bias voltage applied to the APD100, and has the characteristic of rapidly increasing near the breakdown voltage of the APD100, regardless of whether light is incident on the APD100 or not. The multiplication factor characteristic (relationship between the multiplication rate and the reverse bias voltage) also changes with temperature, as shown in FIG. 3.

[0015] It is known that the multiplication factor characteristics for each temperature are similar to each other, and that the multiplication factor characteristics almost match when normalized by the reverse bias voltage at which the multiplication factor near the breakdown voltage becomes very high. Figure 4 is a diagram showing the multiplication factor characteristics of the APD100 when the reverse bias voltage in Figure 3 is normalized by the reverse bias voltage Vd at which the rate of increase near the breakdown voltage becomes very high. By understanding the multiplication factor and reverse bias voltage Vd of the APD, it is possible to obtain a reverse bias voltage at which the multiplication factor becomes a desired multiplication factor (predetermined value) from the multiplication factor characteristics in Figure 4.

[0016] An example of multiplication factor control will be described below. A TIA (Trans Impedance Amplifier) ​​101 converts a current flowing through the APD 100 into a voltage. An ADC (Analog to Digital Converter) 102 converts an analog signal from the TIA 101 into a digital signal. An observation unit 200 observes (measures) an output from the ADC 102. The observation unit 200 increases a reverse bias voltage applied to the APD 100 until the output from the ADC 102 becomes a predetermined amount A on average, and obtains information on the reverse bias voltage Vd when the average value becomes the predetermined amount A and information on the variance of the output of the APD 100. The variance of the output of the APD 100 changes depending on the amount of light incident on the APD 100.

[0017] 5 is a diagram showing a schematic diagram of a received signal (observed signal) in which the output of the APD 100 is a predetermined amount A when the amount of light incident on the APD 100 is small. When the amount of light incident on the APD 100 is small, that is, when there are almost no photons that cause a current to flow, the output of the APD 100 is small. However, there are cases in which the dark current of the APD 100, which occurs very rarely, is amplified to a very high value, and the average value becomes the predetermined amount A. The received signal varies greatly between cases where the output is small and cases where the output is large, and therefore the variance becomes large.

[0018] 6 is a diagram showing a schematic diagram of a received signal in which the output of the APD 100 becomes a predetermined amount A when the amount of light incident on the APD 100 is large. When the amount of light incident on the APD 100 is large, that is, when there are many photons that cause a current to flow, the average value becomes the predetermined amount A without extremely increasing the multiplication factor. The received signal becomes more stable and has less variance compared to the case of FIG. 5.

[0019] 7 is a diagram showing the relationship between the amount of light incident on the APD 100 and the variance of the output of the APD 100 acquired from a received signal. As described above, when the amount of light incident on the APD 100 is small, the variance is large, and when the amount of light incident on the APD 100 is large, the variance is small.

[0020] The background light amount estimating unit 301 estimates information about the amount of light incident on the APD, using information about the variance acquired by the observing unit 200. In this embodiment, the background light amount estimating unit 301 estimates the amount of light incident on the APD 100, which corresponds to the variance acquired by the observing unit 200, using the relationship in FIG.

[0021] The multiplication factor estimation unit 302 estimates a multiplication factor at which the amount of light incident on the APD 100 estimated by the background light amount estimation unit 301 becomes a predetermined amount A. For example, if the predetermined amount A is 1000 and the amount of light incident on the APD 100 is estimated to be 10, the multiplication factor can be estimated to be 100. Note that instead of estimating the multiplication factor at which the predetermined amount A is obtained for each measurement, the multiplication factor may be estimated by referring to a result calculated in advance as shown in FIG.

[0022] The voltage estimation unit 303 estimates a reverse bias voltage that will result in a desired multiplication factor from the multiplication factor estimated by the multiplication factor estimation unit 302, information on the reverse bias voltage Vd acquired by the observation unit 200, and the multiplication factor characteristic of Fig. 4. For example, if the reverse bias voltage Vd acquired by the observation unit 200 is 200 V, the multiplication factor is 1000, and it is desired to control the multiplication factor to 100, the reverse bias voltage is acquired to be 186 V (=200 V × (0.9 / 0.97)) from the multiplication factor characteristic of Fig. 4.

[0023] The voltage control unit 401 applies the reverse bias voltage estimated by the voltage estimation unit 303 to the APD 100, thereby setting the desired multiplication factor.

[0024] An example of the timing at which the multiplication factor control is performed will be described below. The timing at which the multiplication factor control is performed is, for example, the flyback period of the scanning mirror 500. The scanning mirror 500 is a MEMS mirror that can rotate or oscillate around two predetermined rotation axes that are orthogonal to each other. Note that the scanning mirror 500 may be a mirror other than the MEMS mirror.

[0025] 9 is a diagram showing a schematic diagram of a scanning trajectory of the scanning mirror 500. In this embodiment, a scanning method is used in which scanning is performed from a scanning start position along a trajectory like a light line, and when the scanning end position is reached, the scanning returns to the scanning start position along a trajectory like a dark line. The dark line is a blanking period, during which the laser is not emitted, that is, during which distance measurement is not performed (non-measurement period). Note that the scanning trajectory is not limited to the example in FIG. 9. By performing the multiplication factor control of this embodiment during the blanking period, it is possible to control the APD 100 to a desired multiplication factor while maintaining the distance measurement period (measurement period).

[0026] Although it depends on the drive frequency of the scanning mirror 500, since the retrace period is about a few msec, the average value may not reach the predetermined amount A in one process even if the reverse bias voltage applied to the APD 100 is increased. In this case, in the next retrace period, the reverse bias voltage is increased from the value at the end of the previous control until the average value reaches the predetermined amount A. If the average value does not reach the predetermined amount A, the same process is performed in the next retrace period. In this way, by continuing the previous control and performing control until the average value reaches the predetermined amount A, continuous control is possible without stopping measurement.

[0027] The above-mentioned control may be performed continuously while the LiDAR is in operation. In addition, the control may be started in response to a predetermined trigger given to the control unit 400. The trigger may be, for example, a large change in the amount of background light or a change in temperature. [Other Examples] The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-mentioned embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions.

[0028] The disclosure of this embodiment includes the following configurations and methods. (Configuration 1) A receiving device that irradiates an electromagnetic wave onto an object using a scanning mirror and measures a distance to the object based on the electromagnetic wave reflected by the object, APD and an observation unit that observes the output of the APD; a control unit that increases a reverse bias voltage applied to the APD until an observed output of the APD reaches a predetermined amount during a non-measurement period during which the distance is not measured, which occurs during a measurement period during which the distance is measured, and controls the reverse bias voltage using information acquired when the output of the APD reaches the predetermined amount so that a multiplication factor of the APD becomes a predetermined value. (Configuration 2) 2. The receiving device according to claim 1, wherein the information includes information about the reverse bias voltage and information about the multiplication factor when the output of the APD reaches the predetermined amount. (Configuration 3) 3. The receiving device according to configuration 2, wherein the control unit controls the reverse bias voltage using information related to the reverse bias voltage, information related to the multiplication factor, and the predetermined value. (Configuration 4) the observation unit acquires information regarding a dispersion of the output of the APD when the output of the APD reaches the predetermined amount, 4. The receiving device according to any one of configurations 1 to 3, wherein the information includes information about the amount of light incident on the APD, the information corresponding to the information about the dispersion. (Configuration 5) 5. The receiving device according to configuration 4, wherein the information about the multiplication factor corresponds to information about the amount of light incident on the APD. (Configuration 6) 6. The receiving device according to any one of configurations 1 to 5, wherein the non-measurement period is a blanking period of the scanning mirror. (Method 1) A method for controlling a receiving device having an APD, irradiating an electromagnetic wave onto an object using a scanning mirror, and measuring a distance to the object based on the electromagnetic wave reflected by the object, comprising the steps of: increasing a reverse bias voltage applied to the APD during a non-measurement period during which the distance is not measured, occurring during a measurement period during which the distance is measured, until an output of the APD reaches a predetermined amount; and controlling the reverse bias voltage using information acquired when the output of the APD reaches the predetermined amount so that the multiplication factor of the APD becomes a predetermined value. (Configuration 7) A program for causing a computer to execute the control method according to method 1. (Configuration 8) A computer-readable storage medium storing the program according to configuration 7.

[0029] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0030] 100 APD 200 Observation Section 400 Control section 500 Scanning Mirror

Claims

1. A receiving device that irradiates an electromagnetic wave onto an object using a scanning mirror and measures a distance to the object based on the electromagnetic wave reflected by the object, APD and an observation unit for observing an output of the APD; a control unit that increases a reverse bias voltage applied to the APD until an observed output of the APD reaches a predetermined amount during a non-measurement period during which the distance is not measured, which occurs during a measurement period during which the distance is measured, and controls the reverse bias voltage using information obtained when the output of the APD reaches the predetermined amount so that a multiplication factor of the APD becomes a predetermined value.

2. 2. The receiving device according to claim 1, wherein the information includes information on the reverse bias voltage and information on the multiplication factor when the output of the APD reaches the predetermined amount.

3. 3. The receiving device according to claim 2, wherein the control unit controls the reverse bias voltage using information related to the reverse bias voltage, information related to the multiplication factor, and the predetermined value.

4. the observation unit acquires information regarding a dispersion of the output of the APD when the output of the APD reaches the predetermined amount, 3. The receiving apparatus according to claim 1, wherein the information includes information about the amount of light incident on the APD, the information corresponding to the information about the dispersion.

5. 5. The receiving device according to claim 4, wherein the information on the multiplication factor corresponds to information on the amount of light incident on the APD.

6. 3. The receiving device according to claim 1, wherein the non-measurement period is a blanking period of the scanning mirror.

7. A method for controlling a receiving device having an APD, irradiating an electromagnetic wave onto an object using a scanning mirror, and measuring a distance to the object based on the electromagnetic wave reflected by the object, comprising the steps of: increasing a reverse bias voltage applied to the APD during a non-measurement period during which the distance is not measured, occurring during a measurement period during which the distance is measured, until an output of the APD reaches a predetermined amount; and controlling the reverse bias voltage using information acquired when the output of the APD reaches the predetermined amount so that the multiplication factor of the APD becomes a predetermined value.

8. A program for causing a computer to execute the control method according to claim 7.

9. A computer-readable storage medium storing the program according to claim 8.

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