JP7578426B2 - Sensor Device - Google Patents

Description

The present invention relates to a control device and a sensor device.

In recent years, sensor devices such as LiDAR (Light Detection and Ranging) have been developed. The sensor devices are equipped with avalanche diodes that receive electromagnetic waves such as infrared rays.

Patent document 1 describes setting a specific voltage to obtain the optimal multiplication factor of the avalanche diode. Here, a temperature compensation circuit outputs a voltage that corresponds to the temperature gradient of the breakdown voltage of the avalanche diode. This allows the output voltage to be set and temperature compensated.

JP 2006-303524 A

In order to operate an avalanche diode at a desired multiplication factor, it is necessary to estimate a reference operating voltage, such as a breakdown voltage, at which the avalanche diode has the desired multiplication factor. On the other hand, as described in Patent Document 1, temperature compensation may be performed using the temperature gradient of the breakdown voltage of the avalanche diode. However, in this case, the reference operating voltage of the avalanche diode itself is not estimated. For this reason, the avalanche diode cannot be operated at the desired multiplication factor using the estimated reference operating voltage itself.

One example of the problem that the present invention aims to solve is how to operate an avalanche diode at a desired multiplication factor.

The invention described in claim 1 is
A control device for controlling an avalanche diode that receives electromagnetic waves emitted from an emission unit, reflected by a movable reflection unit toward a predetermined scanning range, and reflected by an object present within the scanning range, comprising:
an estimation unit that estimates a reference operating voltage of the avalanche diode at which the avalanche diode has a predetermined multiplication factor;
a setting unit that sets a multiplication factor of the avalanche diode using the reference operating voltage estimated by the estimation unit;
Equipped with
The estimation unit is a control device that sweeps the operating voltage of the avalanche diode to obtain a normalized differential approximation of the output voltage of the avalanche diode with respect to the operating voltage of the avalanche diode, and estimates the reference operating voltage of the avalanche diode from the differential approximation.

The invention described in claim 4 is
An emission unit that emits electromagnetic waves;
a movable reflecting section that reflects the electromagnetic wave emitted from the emitting section toward a predetermined scanning range;
an avalanche diode that receives electromagnetic waves reflected by an object present within the scanning range;
A control device according to any one of claims 1 to 3;
The sensor device includes:

The invention described in claim 5 is
A control device for controlling an avalanche diode,
an estimation unit that estimates a reference operating voltage of the avalanche diode at which the avalanche diode has a predetermined multiplication factor;
a setting unit that sets a multiplication factor of the avalanche diode using the reference operating voltage estimated by the estimation unit;
Equipped with
The estimation unit is a control device that sweeps the operating voltage of the avalanche diode to obtain a normalized differential approximation of the output voltage of the avalanche diode with respect to the operating voltage of the avalanche diode, and estimates the reference operating voltage of the avalanche diode from the differential approximation.

FIG. 1 is a diagram showing a sensor device according to an embodiment. FIG. 4 is a functional block diagram of an estimation unit and a setting unit. FIG. 4 is a circuit diagram of an avalanche diode and a setting unit. 1 is a graph showing an example of the photocurrent i dependency of the relationship between a variable x and a function f(x) expressed by equation (2), which is a simplified version of equation (1); 1 is a graph showing an example of the relationship between a variable x and a function g(x) shown by equation (3). 1 is a graph showing an example of the relationship between the ratio of an operating voltage V _APD to a breakdown voltage V _BR and a multiplication factor M. 1 is a graph for explaining a first example of an event caused by an avalanche of an avalanche diode. 11 is a graph for explaining a second example of an event caused by an avalanche of an avalanche diode.

The following describes an embodiment of the present invention with reference to the drawings. Note that in all drawings, similar components are given similar reference numerals and descriptions are omitted where appropriate.

Figure 1 is a diagram showing a sensor device 10 according to an embodiment.

In FIG. 1, the first direction X and the second direction Y cross each other, specifically, are perpendicular to each other. In FIG. 1, the first direction X is the horizontal direction. The positive direction of the first direction X, which is the direction of the arrow indicating the first direction X, is the left direction when viewed from the movable reflector 120 toward the scanning range of the movable reflector 120, which will be described later. The negative direction of the first direction X, which is the opposite direction to the direction of the arrow indicating the first direction X, is the right direction when viewed from the side where the movable reflector 120 is located toward the scanning range of the movable reflector 120. The second direction Y is the vertical direction. The positive direction of the second direction Y, which is the direction of the arrow indicating the second direction Y, is the upward direction. The negative direction of the second direction Y, which is the opposite direction to the direction of the arrow indicating the second direction Y, is the downward direction.

As will be apparent from the description in this specification, the first direction X may be a direction different from the horizontal direction, and the second direction Y may be a direction different from the vertical direction.

The sensor device 10 includes an emitter 110, a movable reflector 120, an avalanche diode 130, a beam splitter 140, and a control device 20. The control device 20 includes an estimation unit 210 and a setting unit 220. In FIG. 1, the dotted lines extending from the emitter 110, the movable reflector 120, the avalanche diode 130, the beam splitter 140, and the scanning line L indicate electromagnetic waves propagating from the emitter 110, the movable reflector 120, the avalanche diode 130, the beam splitter 140, and the scanning line L. In FIG. 1, the electromagnetic waves reflected from the movable reflector 120 toward the scanning line L are irradiated toward approximately the center of the area in which the scanning line L is formed.

The emission unit 110 emits pulsed electromagnetic waves such as infrared rays at regular intervals. The emission unit 110 is an element, such as a laser diode (LD), that can convert electricity such as a current into electromagnetic waves such as light. The electromagnetic waves emitted from the emission unit 110 pass through the beam splitter 140 and enter the movable reflection unit 120.

The movable reflector 120 reflects the electromagnetic waves emitted from the emission unit 110 toward a predetermined scanning range. The scanning range of the movable reflector 120 is a range that can be irradiated by the electromagnetic waves reflected by the movable reflector 120. The movable reflector 120 is, for example, a two-axis MEMS (Micro Electro Mechanical Systems) mirror. The movable reflector 120 is driven, for example, sinusoidally along the first direction X, and is driven, for example, sawtooth-shaped along the second direction Y at a frequency lower than the sinusoidal wave along the first direction X. That is, the first direction X is the direction of resonant drive of the movable reflector 120, and the second direction Y is the direction of linear drive of the movable reflector 120. As a result, the scanning line L of the movable reflector 120 extends in the second direction Y while meandering in the first direction X.

At least a portion of the electromagnetic waves emitted from the emission unit 110 and reflected by the movable reflection unit 120 is reflected or scattered by an object such as an object present outside the sensor device 10. This electromagnetic wave returns to the movable reflection unit 120, is reflected by the movable reflection unit 120, and is reflected by the beam splitter 140, and is received by the avalanche diode 130. The avalanche diode 130 is an element, such as an APD (avalanche photodiode), that can convert electromagnetic waves such as light into electricity such as current.

The control device 20 controls the avalanche diode 130. Specifically, the control device 20 performs AGC (automatic gain control) of the avalanche diode 130.

The estimation unit 210 and the setting unit 220 are not hardware-based configurations, but rather functional blocks. The estimation unit 210 and the setting unit 220 are realized by any combination of hardware and software, centered on the CPU of any computer, memory, a program loaded into the memory, a storage medium such as a hard disk that stores the program, and a network connection interface. There are various variations in the method and device for realizing this.

The estimation unit 210 estimates the reference operating voltage of the avalanche diode 130 at which the avalanche diode 130 has a predetermined multiplication factor. The reference operating voltage is, for example, the breakdown voltage of the avalanche diode 130. The reference operating voltage may be lower than the breakdown voltage of the avalanche diode 130. The setting unit 220 sets the multiplication factor of the avalanche diode 130 using the reference operating voltage estimated by the estimation unit 210. The estimation unit 210 sweeps the operating voltage of the avalanche diode 130 to obtain a normalized differential approximation of the output voltage of the avalanche diode 130 relative to the operating voltage of the avalanche diode 130, and estimates the reference operating voltage of the avalanche diode 130 from the differential approximation.

By using the differential approximation, the estimation unit 210 can estimate the reference operating voltage such as the breakdown voltage at a higher speed than when the differential approximation is not used. In addition, by using the differential approximation, it is not necessary to increase the voltage of the avalanche diode 130 to a high voltage compared to when the differential approximation is not used. When sweeping the operating voltage of the avalanche diode 130, the higher the multiplication factor, the higher the current flows through the avalanche diode 130, and the higher the temperature of the avalanche diode 130. The longer the time that the current flows through the avalanche diode 130, the higher the temperature of the avalanche diode 130. And the higher the temperature of the avalanche diode 130, the higher the reference operating voltage of the avalanche diode 130. In this embodiment, the reference operating voltage of the avalanche diode 130 can be accurately estimated by estimating the reference operating voltage at a higher speed.

The estimation unit 210 can estimate the reference operating voltage of the avalanche diode 130 at the timing when the scanning line L of the movable reflector 120 passes through at least one of the two outer sides in the second direction Y of the field of view F generated by the movable reflector 120. Estimating the reference operating voltage takes a certain amount of time. Therefore, by using the above timing, which is a relatively long period of time within the scanning range of the movable reflector 120, it becomes easier to estimate the reference operating voltage than by using other timings within the scanning range of the movable reflector 120. However, the estimation unit 210 may estimate the reference operating voltage of the avalanche diode 130 at a timing different from the above timing.

Note that the field of view F is, for example, the FOV (Field Of View) generated by the movable reflector 120.

After the control device 20 performs AGC on the avalanche diode 130, the sensor device 10 may perform at least one of the following: adjustment of the output electromagnetic wave intensity of the emission unit 110 using the AGC-processed avalanche diode 130; and adjustment of the deflection angle of the movable reflector 120 using the AGC-processed avalanche diode 130. For example, the sensor device 10 may perform AGC on the avalanche diode 130, adjustment of the output electromagnetic wave intensity of the emission unit 110, and adjustment of the deflection angle of the movable reflector 120 within one frame of scanning by the movable reflector 120. In this example, for example, the AGC of the avalanche diode 130 may be performed on one of the two outer sides in the second direction Y of the field of view F generated by the movable reflector 120. Also, adjustment of the output electromagnetic wave intensity of the emission unit 110 may be performed on one of the two outer sides in the first direction X of the field of view F generated by the movable reflector 120. Furthermore, the adjustment of the deflection angle of the movable reflector 120 may be performed on the other of the two outer sides in the first direction X of the field of view F generated by the movable reflector 120. Furthermore, the adjustment of the deflection angle of the movable reflector 120 may be performed after the adjustment of the output electromagnetic wave intensity of the emission unit 110. In this case, the adjustment of the deflection angle of the movable reflector 120 can be performed in a state in which the output electromagnetic wave intensity of the emission unit 110 is stable, compared to the case in which the adjustment of the output electromagnetic wave intensity of the emission unit 110 is performed after the adjustment of the deflection angle of the movable reflector 120. The adjustment of the output electromagnetic wave intensity of the emission unit 110 may be performed after the adjustment of the deflection angle of the movable reflector 120.

The estimation unit 210 may estimate the reference operating voltage of the avalanche diode 130 using electromagnetic waves reflected or scattered by the reference reflector 300. This electromagnetic wave returns toward the movable reflector 120 by reflection or scattering by the reference reflector 300, and is received by the avalanche diode 130 after being reflected by the movable reflector 120 and the beam splitter 140 in that order. If the reference operating voltage is estimated using background light, there is a risk that a sufficient amount of light for estimating the reference operating voltage cannot be obtained using only the background light. In contrast, if the electromagnetic wave reflected or scattered by the reference reflector 300 is used, a sufficient amount of light for estimating the reference operating voltage can be obtained compared to the case where background light is used. The estimation unit 210 may estimate the reference operating voltage using background light.

The distance from the movable reflector 120 to the reference reflector 300 is shorter than the distance from the movable reflector 120 to the object. Therefore, the time from the emission of the electromagnetic wave from the emission unit 110, through the reflection of the electromagnetic wave by the reference reflector 300, to the reception of the electromagnetic wave by the avalanche diode 130 is shorter than the time from the emission of the electromagnetic wave from the emission unit 110, through the reflection of the electromagnetic wave by the object, to the reception of the electromagnetic wave by the avalanche diode 130. Therefore, based on the time difference of the signal generated in the avalanche diode 130, the sensor device 10 can distinguish whether the signal generated in the avalanche diode 130 is a signal caused by the reference reflector 300 or a signal caused by the object.

The reference reflector 300 may be provided in the sensor device 10. That is, the sensor device 10 may include the reference reflector 300. Alternatively, the reference reflector 300 may be provided outside the sensor device 10. When the reference reflector 300 is provided in the sensor device 10, the reference reflector 300 may be provided in, for example, a window portion of a housing that houses the components that constitute the sensor device 10, such as the emission portion 110, the movable reflector 120, the avalanche diode 130, and the beam splitter 140, i.e., a portion through which electromagnetic waves pass between the inside and outside of the housing. However, the location where the reference reflector 300 is provided is not limited to the window portion.

Figure 2 is a functional block diagram of the estimation unit 210 and the setting unit 220.

2 , background light P is input to the setting unit 220, and a voltage _Vh is applied. An output voltage _Vout is output from the setting unit 220 in accordance with the background light P and the voltage _Vh . The estimation unit 210 estimates the breakdown voltage _VBR of the avalanche diode 130 using the output voltage _Vout output from the setting unit 220. The setting unit 220 sets the multiplication factor of the avalanche diode 130 using the breakdown voltage _VBR estimated by the estimation unit 210.

Figure 3 is a circuit diagram of the avalanche diode 130 and the setting unit 220.

As shown in FIG. 3, the setting unit 220 is a TIA (transimpedance amplifier) circuit. A voltage V _h is applied to the cathode of the avalanche diode 130 via a resistor with a resistance value R _lim . The anode of the avalanche diode 130 is connected to the inverting input terminal of an operational amplifier U whose non-inverting input terminal is grounded. A current I _out flows through the avalanche diode 130. The operating voltage V _APD of the avalanche diode 130 is V _h -R _lim I _out . A resistor with a resistance value R _f is connected between the inverting input terminal and the output terminal of the operational amplifier U. An output voltage V _out is output from the output terminal of the operational amplifier U via a resistor with a resistance value R ₁ .

ただし、ｉは光電流を示す。 The output voltage V _out of the avalanche diode 130 is expressed by the following equation (1).

Here, i represents a photocurrent.

ただし、ｘ＝Ｖ_ＡＰＤ／Ｖ_ＢＲである。 4 is a graph showing an example of the photocurrent i dependency of the relationship between the variable x and a function f(x) shown by equation (2), which is a simplified version of equation (1). In FIG. 4, functions f(x) of 1.E+00, 1.E+01, 1.E+02, 1.E+03, and 1.E+04 are shown for the photocurrent i.

Here, x=V _APD /V _BR .

Figure 5 is a graph showing an example of the relationship between the variable x and the function g(x) shown in equation (3).

By normalizing the function f(x) that changes with the photocurrent i and performing forward differential approximation, the following equation (3) is obtained.

In the example shown in Fig. 5, g(x) = 1.E + 00, and the operating voltage V _APD corresponding to x where the first derivative of g(x) is positive can be estimated as the breakdown voltage V _BR . Note that, although the forward differential approximation is used in the example shown in Fig. 5, a differential approximation different from the forward differential approximation, for example, a backward differential approximation or a central differential approximation, may be used.

6 is a graph showing an example of the relationship between the ratio of the operating voltage V _APD to the breakdown voltage V _BR and the multiplication factor M. This relationship is constant regardless of the temperature of the avalanche diode 130.

Figure 7 is a graph for explaining a first example of an event caused by an avalanche of the avalanche diode 130. In Figure 7, the horizontal axis of the graph represents time. The vertical axis of the graph represents the strength of the signal generated in the avalanche diode 130.

Avalanche-induced events occur when the multiplication factor of the avalanche diode 130 is high, i.e., when the operating voltage of the avalanche diode 130 is high. In the example shown in Figure 7, four avalanche-induced events occur in a situation where there is almost no DC (direct current) component.

The estimation unit 210 may monitor events caused by avalanches and estimate a reference operating voltage such as a breakdown voltage. Specifically, the estimation unit 210 can estimate the reference operating voltage by counting events caused by avalanches.

Figure 8 is a graph illustrating a second example of an event caused by an avalanche of the avalanche diode 130. The example shown in Figure 8 is similar to the example shown in Figure 7, except for the following points.

As shown in FIG. 8, even in a situation where a DC component is present, a peak occurs due to an event caused by avalanche. In this case, the estimation unit 210 may also estimate the reference operating voltage by monitoring the events caused by avalanche. There is a correlation between the events caused by avalanche and the reference operating voltage. Specifically, the more events caused by avalanche, the higher the reference operating voltage.

The above describes the embodiments with reference to the drawings, but these are merely examples of the present invention, and various configurations other than those described above can also be adopted.

For example, in the embodiment, the sensor device 10 is a LiDAR. That is, the avalanche diode 130 receives electromagnetic waves emitted from the emission unit 110, reflected by the movable reflection unit 120 toward a predetermined scanning range, and reflected by an object present within the scanning range. However, the control device 20 may control an avalanche diode used other than the LiDAR.
Below, examples of reference forms are given.
1. A control device for controlling an avalanche diode that receives electromagnetic waves emitted from an emission unit, reflected by a movable reflection unit toward a predetermined scanning range, and reflected by an object present within the scanning range, comprising:
an estimation unit that estimates a reference operating voltage of the avalanche diode at which the avalanche diode has a predetermined multiplication factor;
a setting unit that sets a multiplication factor of the avalanche diode using the reference operating voltage estimated by the estimation unit;
Equipped with
The control device, wherein the estimation unit obtains a normalized differential approximation of the output voltage of the avalanche diode with respect to the operating voltage of the avalanche diode by sweeping the operating voltage of the avalanche diode, and estimates the reference operating voltage of the avalanche diode from the differential approximation.
2. In the control device according to 1.,
The control device, wherein the estimation unit estimates the reference operating voltage by monitoring an event caused by an avalanche of the avalanche diode.
3. In the control device according to 1 or 2,
a scanning line of the movable reflector extends in a second direction intersecting the first direction while meandering in a first direction,
A control device, wherein the estimation unit estimates the reference operating voltage of the avalanche diode at a timing when a scanning line of the movable reflector passes through at least one of the two outer sides in the second direction of a field of view generated by the movable reflector.
4. An emission unit that emits electromagnetic waves;
a movable reflecting section that reflects the electromagnetic wave emitted from the emitting section toward a predetermined scanning range;
an avalanche diode that receives electromagnetic waves reflected by an object present within the scanning range;
A control device according to any one of 1. to 3.
A sensor device comprising:
5. A control device for controlling an avalanche diode, comprising:
an estimation unit that estimates a reference operating voltage of the avalanche diode at which the avalanche diode has a predetermined multiplication factor;
a setting unit that sets a multiplication factor of the avalanche diode using the reference operating voltage estimated by the estimation unit;
Equipped with
The control device, wherein the estimation unit obtains a normalized differential approximation of the output voltage of the avalanche diode with respect to the operating voltage of the avalanche diode by sweeping the operating voltage of the avalanche diode, and estimates the reference operating voltage of the avalanche diode from the differential approximation.

10 Sensor device 20 Control device 110 Emitter 120 Movable reflector 130 Avalanche diode 140 Beam splitter 210 Estimator 220 Setting unit 300 Reference reflector F Field of view L Scanning line X First direction Y Second direction

Claims (2)

An emission unit that emits electromagnetic waves;
a movable reflecting section that reflects the electromagnetic wave emitted from the emitting section toward a predetermined scanning range;
an avalanche diode that receives electromagnetic waves reflected by an object present within the scanning range;
A control device for controlling the avalanche diode;
Equipped with
The control device includes:
an estimation unit that estimates a reference operating voltage of the avalanche diode at which the avalanche diode has a predetermined multiplication factor;
a setting unit that sets a multiplication factor of the avalanche diode using the reference operating voltage estimated by the estimation unit;
Equipped with
the estimation unit sweeps an operating voltage of the avalanche diode to obtain a normalized differential approximation of an output voltage of the avalanche diode with respect to the operating voltage of the avalanche diode, and estimates the reference operating voltage of the avalanche diode from the differential approximation;
In the first derivative of the difference approximation, a value corresponding to the operating voltage estimated by the estimator as the reference operating voltage is positive,
The sensor device has a TIA circuit connected to the anode of the avalanche diode. 2. The sensor device according to claim 1 ,
a scanning line of the movable reflector extends in a second direction intersecting the first direction while meandering in a first direction,
the estimation unit estimates the reference operating voltage of the avalanche diode at a timing when a scanning line of the movable reflector passes at least one of both outer sides in the second direction of a field of view generated by the movable reflector.
Sensor device.

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