Light receiving device, signal processing method for light receiving device, and distance measuring device

Abstract

A light-receiving device according to the present disclosure includes a light-receiving unit including an array of a plurality of photon-counting type light-receiving elements for receiving light from an object, an adding unit for adding values of the plurality of light-receiving elements at a predetermined time to obtain a pixel value, and a logarithmic transformation processing unit for transforming the pixel value into a logarithmic value or an approximate value thereof to obtain logarithmic representation data. The light-receiving device receives pulse light reflected from an object, the pulse light being based on a photon-counting type light-receiving element for receiving light emitted from a light source unit and reflected from an object.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a light-receiving device, a signal processing method for a light-receiving device, and a distance measuring device. BACKGROUND

[0002] A light-receiving device includes an element that generates a signal in response to photonic light reception as a light-receiving element. In this type of light-receiving device, as a measurement method for measuring a distance to an object to be measured, a time-of-flight (ToF) method is used to measure an amount of time until pulsed light emitted from a light source unit toward an object to be measured is reflected by the object to be measured and returns.

[0003] An example of an element that generates a signal in response to photonic light reception includes a photodetector having a plurality of single-photon avalanche diode (SPAD) elements arranged in a plane (see, for example, Patent Literature 1). In this type of distance measuring device, values of the plurality of SPAD elements are added together to serve as a pixel value; however, in order to capture reflected light by sampling a pixel value after laser emission from a light source unit, the pixel value is added to a histogram having a number of bins corresponding to a sampling time.

[0004] Reflected light from an object to be measured is diffused, and its intensity is inversely proportional to the square of the distance. Therefore, by accumulating (adding) a histogram of reflected light based on a plurality of laser emissions, the S / N is improved, and weak reflected light from a farther object to be measured can be discriminated.

[0005] LIST OF CITATIONS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: Japanese Patent Application Publication No. 2018-169384 SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] As described above, in the case of accumulating a histogram of reflected light based on a plurality of emitted pulsed lasers, a pixel value of intense reflected light from a relatively close measurement object is large, and a dynamic range of a number of bins corresponding to a near distance of the histogram increases each time the histogram is accumulated. On the other hand, reflected light from a relatively distant measurement object is weak in inverse proportion to the square of the distance, and a dynamic range of a number of bins corresponding to a far distance of the histogram is small. Therefore, in the case of a histogram in which all numbers of bins are stored as a fixed-length bit depth representation, a capacity of a memory for storing a histogram of reflected light based on a plurality of emitted pulsed lasers increases.

[0010] An object of the present disclosure is to provide an optical receiving device capable of increasing a dynamic range of a histogram over time or reducing a memory capacity, a signal processing method thereof, and a distance measuring device including the same.

[0011] Solution to the problem

[0012] An optical receiving device of the present disclosure for achieving the above object,

[0013] comprises:

[0014] a light receiving unit having a plurality of photon counting type light receiving elements that receive light from an object;

[0015] an adding unit configured to add values of a plurality of the light receiving elements at a predetermined time to use a result as a pixel value; and

[0016] a logarithmic transformation processing unit configured to transform the pixel value obtained as a result of the addition by the adding unit into a logarithmic value or an approximate value thereof to use the resulting value as logarithmic representation data for distance measurement calculation; wherein

[0017] reflective light from an object to be measured is received based on pulsed light applied by a light source unit.

[0018] Further, a signal processing method of an optical receiving device of the present disclosure for achieving the above object, the optical receiving device comprising,

[0019] a light receiving unit having a plurality of photon counting type light receiving elements that receive light from an object; and the optical receiving device receives reflective light from an object to be measured based on pulsed light applied by a light source unit, the signal processing method comprising:

[0020] in signal processing on the optical receiving device,

[0021] adding values of a plurality of the light receiving elements at a predetermined time to use a result as a pixel value; and

[0022] Next, the pixel value is converted into a logarithmic value or an approximate value thereof to use the resulting value as logarithmic representation data for distance measurement calculation.

[0023] Further, a distance measuring device of the present disclosure for achieving the above object,

[0024] comprises:

[0025] a light source unit configured to apply pulsed light to an object to be measured; and

[0026] A light receiving device is configured to receive reflected light from the object to be measured based on the pulse light applied by the light source unit; wherein,

[0027] light receiving device,

[0028] include,

[0029] a light receiving unit having a plurality of photon counting type light receiving elements that receive light from a subject;

[0030] an adding unit configured to add the values ​​of the plurality of light receiving elements at a predetermined time to use the result as a pixel value, and

[0031] A logarithmic conversion processing unit is configured to convert the pixel value obtained as the addition result by the adding unit into a logarithmic value or an approximate value thereof to use the obtained value as logarithmic representation data for distance measurement calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 1 is a block diagram showing an example of the configuration of a light receiving device and a distance measuring device which are premises of the present disclosure.

[0033] Figure 2 This is a diagram for explaining the processing of the adding unit in the optical receiving device.

[0034] Figure 3A 、 Figure 3B and Figure 3C It is an explanatory diagram of a histogram of reflected light at the time of first laser emission.

[0035] Figure 4A 、 Figure 4B and Figure 4C It is an explanatory diagram of a histogram of reflected light when the second laser beam is emitted.

[0036] Figure 5A 、 Figure 5B and Figure 5C It is an explanatory diagram of a histogram of reflected light at the time of emission of the third laser beam.

[0037] FIG6 is a diagram showing a cumulative histogram of a linear representation (No. 1), Figure 6A shows the cumulative histogram for the case of one addition, and Figure 6B A cumulative histogram in the case of four additions is shown.

[0038] FIG7 is a diagram showing a cumulative histogram of linear representation (No. 2), Figure 7A shows the cumulative histogram for the case of 16 additions, and Figure 7B A smoothed histogram is shown in the case of 16 additions.

[0039] Figure 8A and Figure 8B is a graph showing the cumulative of the histogram of the random number of the normal distribution and the fixed value.

[0040] Figure 9A is a waveform graph showing the cumulative of the logarithm of the histogram and the cumulative of the logarithm of the histogram in the case of the conventional technology, Figure 9B is a waveform graph showing the cumulative of the logarithm of the histogram of the value obtained by subtracting the arithmetic mean of the ambient light and the cumulative of the logarithm of the pixel value of the histogram of the value obtained by subtracting the arithmetic mean of the ambient light in the case of the conventional technology.

[0041] Figure 10 is a waveform graph showing the cumulative of the logarithm of the histogram and the cumulative of the logarithm of the pixel value of the histogram of the logarithmic representation in the case of the technology according to the present disclosure.

[0042] Figure 11 is a waveform graph showing the cumulative of the logarithm of the histogram of the value obtained by subtracting the arithmetic mean of the ambient light and the cumulative of the logarithm of the pixel value of the histogram of the logarithmic representation of the value obtained by subtracting the arithmetic mean of the ambient light in the case of the technology according to the present disclosure.

[0043] Figure 12 is a block diagram showing a configuration example of the light receiving device and the distance measuring device of Example 1 according to the first embodiment of the present disclosure.

[0044] Figure 13 is a flowchart describing a flow of a signal processing method in the light receiving device according to Example 1.

[0045] Figure 14 is a block diagram showing a schematic configuration example of a light receiving unit in the light receiving device according to Example 1.

[0046] Figure 15 is a schematic view showing a schematic configuration example of a SPAD array unit of the light receiving unit.

[0047] Figure 16 is a circuit diagram showing a configuration example of a circuit of a pixel of the light receiving unit.

[0048] Figure 17 is a block diagram showing a configuration example of an adding unit in the light receiving device according to Example 1.

[0049] Figure 18 is a block diagram showing a configuration example of a logarithmic conversion processing unit in the light receiving device according to Example 1.

[0050] Figure 19 is a block diagram showing a configuration example of an ambient light estimation processing unit of the logarithmic representation in the light receiving device according to Example 1.

[0051] Figure 20 is an explanatory diagram of a calculation process in the ambient light estimation processing unit.

[0052] Figure 21 is a block diagram showing a configuration example of a log representation histogram addition processing unit in the light receiving apparatus according to Example 1.

[0053] Figure 22 is an explanatory diagram of a log transformation and an inverse transformation.

[0054] Figure 23 is a diagram showing source code of a log transformation and an inverse transformation circuit described in a hardware language Verilog HDL.

[0055] Fig. 24 is a waveform chart (No. 1) of each unit in the light receiving apparatus according to Example 1, Figure 24A showing an output waveform of an addend, and Figure 24B showing an output waveform of a log transformation unit.

[0056] Fig. 25 is a waveform chart (No. 2) of each unit in the light receiving apparatus according to Example 1, Figure 25A showing an output waveform of a histogram addition processing unit, and Figure 25B showing an output waveform of a smoothing filter.

[0057] Figure 26 is a waveform chart (No. 3) of each unit in the light receiving apparatus according to Example 1, and shows an output waveform of a log transformation unit.

[0058] Fig. 27 is a graph (No. 1) showing a cumulative histogram of a log representation for a case where the ambient light arithmetic mean is not subtracted from the pixel value, Figure 27A showing a cumulative histogram in the case of one addition, and Figure 27B showing a cumulative histogram in the case of four additions.

[0059] Fig. 28 is a graph (No. 2) showing a cumulative histogram of a log representation for a case where the ambient light arithmetic mean is not subtracted from the pixel value, Figure 28A showing a cumulative histogram in the case of 16 additions, and Figure 28B showing a smoothed histogram in the case of 16 additions.

[0060] Fig. 29 is a graph (No. 1) showing a cumulative histogram of a log representation for a case where the ambient light arithmetic mean is subtracted from the pixel value, Figure 29A showing a cumulative histogram in the case of one addition, and Figure 29B showing a cumulative histogram in the case of four additions.

[0061] Fig. 30 is a graph (No. 2) showing a cumulative histogram of a logarithmic representation in the case where the arithmetic mean value of the ambient light is subtracted from the pixel values, Figure 30A A cumulative histogram in the case of 16 additions is shown, and Figure 30B A smoothed histogram in the case of 16 additions is shown.

[0062] Figure 31 is a block diagram showing a configuration example of a light-receiving device and a distance measuring device according to Example 2 of the first embodiment of the present disclosure.

[0063] Figure 32A is a block diagram showing a configuration example of a logarithmic transformation processing unit in the light-receiving device according to Example 2, Figure 32B is a block diagram showing a configuration example of an ambient light estimation processing unit by a geometric mean value in the light-receiving device according to Example 2.

[0064] Figure 33 is a block diagram showing a configuration example of a logarithmic representation histogram addition processing unit in the light-receiving device according to Example 2.

[0065] Figure 34 is a block diagram showing a configuration example of a light-receiving device and a distance measuring device according to Example 3 of the first embodiment of the present disclosure.

[0066] Figure 35 is a block diagram showing a first circuit example of a circuit portion that calculates a change in the ambient light intensity estimation and the logarithmic representation in the ambient light estimation processing unit according to Example 3.

[0067] Figure 36 is a block diagram showing a second circuit example of a circuit portion that calculates a change in the ambient light intensity estimation and the logarithmic representation in the ambient light estimation processing unit according to Example 3.

[0068] Fig. 37 is a block diagram showing a circuit example of a logarithmic transformation unit according to Example 4, Figure 37A a circuit configuration according to a first specific example is shown, and Figure 37B a circuit configuration according to a second specific example is shown.

[0069] Fig. 38 is a graph (No. 1) showing a logarithm of a value obtained by subtracting a minimum value from a cumulative value of a histogram of pixel values in a logarithmic representation, Figure 38A a logarithm in the case of one addition is shown, and Figure 38B a logarithm in the case of four additions is shown.

[0070] Fig. 39 is a graph (No. 2) showing a logarithm of a value obtained by subtracting a minimum value from a cumulative value of a histogram of pixel values in a logarithmic representation,Figure 39A The logarithm in the case of 16 additions is shown, and Figure 39B The logarithm in the case of 32 additions is shown.

[0071] Fig. 40 is a diagram showing the logarithm of the value obtained by subtracting the minimum value from the cumulative value of the histogram of the pixel values in the case of the logarithmic representation of the value obtained by subtracting the arithmetic mean value of the ambient light (No. 1), Figure 40A The logarithm in the case of one addition is shown, Figure 40B The logarithm in the case of four additions is shown.

[0072] Fig. 41 is a diagram showing the logarithm of the value obtained by subtracting the minimum value from the cumulative value of the histogram of the pixel values in the case of the logarithmic representation of the value obtained by subtracting the arithmetic mean value of the ambient light (No. 2), Figure 41A The logarithm in the case of 16 additions is shown, and Figure 41B The logarithm in the case of 32 additions is shown.

[0073] Figure 42 Fig. 42 is a block diagram showing a configuration example of a histogram addition processing unit of the logarithmic representation according to Example 5.

[0074] Figure 43 Fig. 43 is a diagram showing a flow of the differential encoding of the cumulative histogram of the logarithmic representation.

[0075] Figure 44A Fig. 44 is a diagram showing the data size in the case where 2048 groups of histograms are stored in the SRAM without being compressed, Figure 44B Fig. 45 is a diagram showing the data size in the case where the differential encoding is performed.

[0076] Figure 45 Fig. 46 is a block diagram showing a configuration example of an encoding circuit.

[0077] Figure 46 Fig. 47 is a block diagram showing a configuration example of a decoding circuit.

[0078] Figure 47 Fig. 48 is a diagram showing the cumulative histogram of the logarithmic representation in the case of 16 additions without subtracting the geometric mean value of the ambient light.

[0079] Figure 48 Fig. 49 is a diagram showing the cumulative histogram of the logarithmic representation in the case of 16 additions with the geometric mean value of the ambient light subtracted.

[0080] Figure 49A Fig. 50 is a diagram showing the difference between the geometric mean value and the arithmetic mean value in the case where the average value of the noise is found by synchronous addition, and Figure 49B Fig. 51 is a diagram showing the histogram of the data values.

[0081] Figure 50A FIG. 6 is a graph showing the difference between the geometric mean value and the arithmetic mean value in the case where the average value in the time direction is taken. Figure 50B FIG. 7 is a graph showing a histogram of data values.

[0082] Figure 51 FIG. 8 is a schematic diagram showing a schematic configuration example of a distance measuring device according to a second embodiment of the present disclosure.

[0083] Figure 52 FIG. 9 is a block diagram showing an example of a schematic configuration of a vehicle control system as an example of a moving object control system to which the technology according to the present disclosure can be applied.

[0084] Figure 53 FIG. 10 is a diagram showing an example of the mounting positions of the imaging section and the outside-vehicle information detecting section. DETAILED DESCRIPTION

[0085] Hereinafter, modes for executing the technology according to the present disclosure (hereinafter, referred to as "embodiments") will be described in detail with reference to the drawings. The technology according to the present disclosure is not limited to the embodiments, and various numerical values and the like in the embodiments are examples. In the following description, the same reference numerals are used for the same elements or elements having the same function, and redundant description is omitted. Note that the description is given in the following order.

[0086] 1. Description of Light Receiving Device, Signal Processing Method for Light Receiving Device, and Distance Measuring Device of the Present Disclosure

[0087] 2. Light Receiving Device and Distance Measuring Device as a Premise of the Present Disclosure

[0088] 2-1. Configuration Example of System

[0089] 2-2. Principle of Distance Measurement by ToF Sensor

[0090] 2-3. Configuration Example of Light Source Unit

[0091] 2-4. Configuration Example of Light Receiving Device

[0092] 2-5. Problems of Conventional Technology

[0093] 3. First Embodiment of the Present Disclosure (Example of Distance Measuring Device of Flash Type)

[0094] 3-1. Example 1 (Example of Obtaining Logarithmic Representation Data after Subtracting a Predetermined Value from Pixel Value)

[0095] 3-1-1. Configuration Example of System

[0096] 3-1-2. An example of a schematic configuration of a light-receiving unit

[0097] 3-1-2-1. An example of a schematic configuration of a SPAD array unit

[0098] 3-1-2-2. An example of a circuit configuration of a SPAD pixel

[0099] 3-1-2-3. An example of a schematic operation of a SPAD pixel

[0100] 3-1-3. An example of a configuration of an addition unit

[0101] 3-1-4. An example of a configuration of a logarithmic conversion processing unit

[0102] 3-1-5. An example of a configuration of an ambient light estimation processing unit in a logarithmic representation

[0103] 3-1-6. An example of a configuration of a histogram addition processing unit in a logarithmic representation

[0104] 3-2. Example 2 (an example of obtaining logarithmic representation data by converting a pixel value into a logarithmic value or an approximate value thereof and then subtracting a predetermined value in a logarithmic representation)

[0105] 3-2-1. An example of a configuration of a system

[0106] 3-2-2. An example of a configuration of a logarithmic conversion processing unit

[0107] 3-2-3. An example of a configuration of an ambient light estimation processing unit in a logarithmic representation

[0108] 3-2-4. An example of a configuration of a histogram addition processing unit in a logarithmic representation

[0109] 3-3. Example 3 (an example of calculating an arithmetic mean and a variance of an ambient light estimation processing in a logarithmic representation)

[0110] 3-3-1. An example of a configuration of a system

[0111] 3-3-2. An example of a method for calculating an arithmetic mean and a variance of an ambient light in a logarithmic representation

[0112] 3-3-3. An example of a circuit for calculating an arithmetic mean and a variance of an ambient light in a logarithmic representation

[0113] 3-4. Example 4 (a specific example of a logarithmic conversion unit in a light-receiving device according to Example 1 / 2)

[0114] 3-4-1. A first circuit example

[0115] 3-4-2. Second circuit example

[0116] 3-5. Example 5 (Example of reducing memory capacity by compressing data on a cumulative histogram expressed in a logarithm)

[0117] 3-5-1. Configuration example of system

[0118] 3-5-2. Configuration example of encoding circuit

[0119] 3-5-3. Configuration example of decoding circuit

[0120] 3-6. Functional effects of first embodiment

[0121] 4. Second embodiment of the present disclosure (Example of distance measuring device of scanning type)

[0122] 4-1. Configuration example of system of distance measuring device

[0123] 4-2. Functional effects of second embodiment

[0124] 5. Application example of technology according to the present disclosure

[0125] 5-1. Example of moving object

[0126] 6. Configurations in which the present disclosure can be employed

[0127] <Description of light-receiving device, signal processing method for light-receiving device, and distance measuring device>

[0128] In the light-receiving device, the signal processing method therefor, and the distance measuring device of the present disclosure, a logarithmic conversion processing unit converts a value obtained by subtracting a predetermined value from a pixel value into a logarithmic value or an approximate value thereof to use the resulting value as logarithmic representation data for ranging calculation, and in a case where the predetermined value is greater than the pixel value, the logarithmic conversion processing unit performs conversion processing on a value obtained as a result of subtraction that is zero (0).

[0129] In the light-receiving device, the signal processing method therefor, and the distance measuring device of the present disclosure including the above-described preferred configurations, assuming that the predetermined value is an ambient light intensity estimation value obtained by adding a predetermined addend to a value obtained by multiplying an arithmetic mean value of ambient light by a predetermined multiplier, an ambient light estimation processing unit is included that is configured to calculate the arithmetic mean value of the ambient light in a logarithmic representation based on the pixel value to estimate the ambient light intensity. Then, the logarithmic conversion processing unit subtracts the ambient light intensity estimated by the ambient light estimation processing unit from the pixel value to use the result as the logarithmic representation data for ranging calculation.

[0130] Alternatively, in the light-receiving apparatus, the signal processing method thereof, and the distance measuring apparatus of the present disclosure including the above-described preferred configuration, the logarithmic conversion processing unit subtracts data obtained as a result of conversion from a predetermined value to a logarithmic value or an approximate value thereof from data obtained as a result of conversion from a pixel value to a logarithmic value or an approximate value thereof, and uses the resultant data as logarithmic representation data for range-finding calculation.

[0131] Further, in the light-receiving apparatus, the signal processing method thereof, and the distance measuring apparatus of the present disclosure including the above-described preferred configuration, assuming that the predetermined value is an ambient light intensity estimation value obtained by adding a predetermined addend to a value obtained by multiplying a geometric mean value of ambient light by a predetermined multiplier, an ambient light estimation processing unit configured to calculate the geometric mean value of the ambient light in a logarithmic representation based on the pixel value to estimate the ambient light intensity. Then, the logarithmic conversion processing unit converts the ambient light intensity estimated by the ambient light estimation processing unit to a logarithmic value or an approximate value thereof.

[0132] Further, in the light-receiving apparatus, the signal processing method thereof, and the distance measuring apparatus of the present disclosure including the above-described preferred configuration, a histogram addition processing unit configured to associate a time of flight from emission of pulsed light applied by the light source unit to return of reflected light with a group number of a histogram, and store logarithmic representation data calculated based on the pixel value sampled at each time as a count value of the group number corresponding to the time.

[0133] Further, in the light-receiving apparatus, the signal processing method thereof, and the distance measuring apparatus of the present disclosure including the above-described preferred configuration, the histogram addition processing unit adds and updates the histogram the logarithmic representation data over time from reflection of light from the object to be measured based on emission of pulsed light applied by the light source unit multiple times and the count value corresponding to the group number of time.

[0134] Further, in the light-receiving apparatus, the signal processing method thereof, and the distance measuring apparatus of the present disclosure including the above-described preferred configuration, the histogram addition processing unit generates a histogram obtained by accumulating count values calculated by receiving pixel values obtained based on reflection of light from emission of pulsed light applied by the light source unit multiple times, or, alternatively, subtracts a value calculated using pixel values sampled over multiple times in a predetermined measurement period from the pixel values as the predetermined value, and adds logarithmic representation data calculated by the subtraction as the count value of the group number of the histogram.

[0135] Further, in the light-receiving apparatus, the signal processing method thereof, and the distance measuring apparatus of the present disclosure including the above-described preferred configurations, the reflected light detection unit is configured to detect a peak value of each reflected light by performing amplitude comparison between count values of a histogram using a logarithmic representation and calculate a distance based on a time corresponding to a group number at a rising start of the peak value.

[0136] Further, in the light-receiving apparatus, the signal processing method thereof, and the distance measuring apparatus of the present disclosure including the above-described preferred configurations, the ambient light estimation processing unit is configured as follows. Specifically, the ambient light estimation processing unit calculates an approximation value S of a logarithmic value of a sum of pixel values while maintaining a logarithmic representation of logarithmic representation data LogD obtained by transforming pixel values sampled at a plurality of times in a predetermined measurement period into logarithmic values or approximation values of logarithmic values using a predetermined approximation expression. Next, the ambient light estimation processing unit calculates an approximation value μ of an arithmetic mean value from a value obtained by subtracting a logarithmic value of the number N of samples or an approximation value thereof from the approximation value S. Next, the ambient light estimation processing unit calculates an approximation value SS of a logarithmic value of a sum obtained by squaring the pixel values while maintaining a logarithmic representation of a value obtained by doubling the logarithmic representation data LogD using the predetermined approximation expression. Next, the ambient light estimation processing unit calculates a value MM obtained by subtracting a logarithmic value of the number N of samples or an approximation value thereof from the approximation value SS. Next, the ambient light estimation processing unit calculates an approximation value V of a variance of the ambient light using the approximation value μ of the arithmetic mean value and the value MM. Then, the ambient light estimation processing unit outputs an ambient light intensity estimation value obtained by adding a predetermined addend to a value obtained by multiplying the approximation value μ of the arithmetic mean value by a predetermined multiplier and an approximation value of a standard deviation of the ambient light calculated from the approximation value V of the variance.

[0137] Further, in the light-receiving apparatus, the signal processing method thereof, and the distance measuring apparatus of the present disclosure including the above-described preferred configurations, the ambient light estimation processing unit transforms a sum obtained by summing pixel values sampled at a plurality of times in a predetermined measurement period into a logarithmic value or an approximation value thereof and outputs an image in which the transformed logarithmic representation data is used as pixel values.

[0138] Further, in the light-receiving apparatus, the signal processing method thereof, and the distance measuring apparatus of the present disclosure including the above-described preferred configurations, the ambient light estimation processing unit calculates an approximation value of a logarithmic value of a sum of pixel values while maintaining a logarithmic representation of logarithmic representation data obtained by transforming pixel values sampled at a plurality of times in a predetermined measurement period into logarithmic values or approximation values of logarithmic values using a predetermined approximation expression and outputs an image in which the approximation value is used as pixel values.

[0139] Further, in the light-receiving apparatus, the signal processing method thereof, and the distance measuring apparatus of the present disclosure including the above-described preferred configuration, a logarithmic transformation unit configured to further logarithmically transform and compress the logarithmically represented cumulative histogram is included, or alternatively, a logarithmic transformation unit configured to further logarithmically transform and compress the logarithmically represented cumulative histogram after subtracting the minimum value thereof is included.

[0140] Further, in the light-receiving apparatus, the signal processing method thereof, and the distance measuring apparatus of the present disclosure including the above-described preferred configuration, the histogram addition processing unit has a data compression / decompression function by differential encoding before and after the storage of the logarithmically represented data in the memory.

[0141] Further, in the light-receiving apparatus, the signal processing method thereof, and the distance measuring apparatus of the present disclosure including the above-described preferred configuration, the light-receiving element includes an avalanche photodiode operated in a Geiger mode.

[0142] [Light-receiving apparatus and distance measuring apparatus as a premise of the present disclosure]

[0143] Figure 1 A block diagram showing an example of a configuration of a light-receiving apparatus and a distance measuring apparatus as a premise of the present disclosure is shown. Here, the light-receiving apparatus and the distance measuring apparatus as a premise of the present disclosure mean a light-receiving apparatus and a distance measuring apparatus before application of the technology according to the present disclosure described later. Hereinafter, the light-receiving apparatus and the distance measuring apparatus as a premise of the present disclosure are described as a light-receiving apparatus and a distance measuring apparatus according to a conventional technology.

[0144] [Configuration example of system]

[0145] The distance measuring apparatus 1 according to the conventional technology includes a light source unit 20 that applies light to a measurement target object 10, a light-receiving apparatus 30 that receives reflected light from the measurement target object 10 based on pulsed light applied by the light source unit 20, and a host computer 40.

[0146] The light source unit 20 includes, for example, a laser source that emits pulsed laser light having a peak wavelength in an infrared wavelength region.

[0147] The light-receiving apparatus 30 is a ToF sensor that employs a ToF method as a measurement method for measuring a distance d to the measurement target object 10, measures a time of flight from when pulsed laser light is emitted from the light source unit 20 to when the pulsed laser light reflected by the measurement target object 10 returns, and obtains the distance d based on the time of flight.

[0148] [Distance measuring principle of ToF method sensor]

[0149] Assuming that t [seconds] is a round-trip time from when the pulsed laser is emitted from the light source unit 20 toward the object to be measured 10 to when the reflected laser returns to the light receiving device 30, the speed of light C is C≈300 million meters / second, so that the distance d between the object to be measured 10 and the distance measuring device 1 can be estimated as in the following equation.

[0150] d = C x (t / 2)

[0151] For example, when the reflected light is sampled at 1 gigahertz (GHz), the number of bins of the histogram is the number of SPAD elements of each pixel that detects light in a period of 1 nanosecond. Then, the distance measurement resolution is 15 cm / bin.

[0152] For example, in a case where the distance measuring device 1 is installed on a car or the like and is used, the host 40 can be an engine control unit (ECU) installed on the car or the like. Further, in a case where the distance measuring device 1 is installed on an autonomous mobile robot (for example, a home pet robot) or an autonomous mobile object (for example, a robot vacuum cleaner, a pilotless airplane, or a following transport robot) and is used, the host 40 can be a control device or the like that controls the autonomous mobile object.

[0153] [Configuration example of light source unit]

[0154] The light source unit 20 includes, for example, one or a plurality of semiconductor laser diodes, and emits pulsed laser light L1 having a predetermined time width with a predetermined emission period. The light source unit 20 emits the pulsed laser light L1 at least toward an angle range equal to or greater than the angle of view of the light receiving surface of the light receiving device 30. Further, the light source unit 20 emits the laser light L1 having a time width of 1 nanosecond with a period of, for example, 1 gigahertz (GHz). For example, in a case where the object to be measured 10 exists within the distance measurement range, the laser light L1 emitted from the light source unit 20 is reflected by the object to be measured 10 and is incident on the light receiving surface of the light receiving device 30 as reflected light L2.

[0155] [Configuration example of light receiving device]

[0156] The light receiving device 30, which is a ToF sensor, includes a control unit 31, a light receiving unit 32, an addition unit 33, a histogram addition processing unit 34, an ambient light estimation processing unit 35, a smoothing filter 36, a reflected light detection unit 37, and an external output interface (I / F) 38.

[0157] For example, the control unit 31 is implemented by an information processing device such as a central processing unit (CPU), and controls each functional unit in the light receiving device 30.

[0158] Although details are described later, for example, the light-receiving unit 32 includes a photon-counting type light-receiving element, such as a single-photon avalanche diode (SPAD) array unit, that receives light from an object, in which pixels each including a SPAD element as a light-receiving element, hereinafter referred to as "SPAD pixels", are two-dimensionally arranged in a matrix (lattice), where the light-receiving element is an example of an avalanche photodiode that operates in a Geiger mode. A plurality of SPAD pixels in the SPAD array unit are grouped into a plurality of pixels each including one or more SPAD pixels.

[0159] One group pixel corresponds to one pixel in the distance measurement image. Thus, the number of SPAD pixels (number of SPAD elements) and the shape of the region that constitute one pixel determine the number of pixels of the entire light-receiving device 30, and thus, the resolution of the distance measurement image.

[0160] After the light source unit 20 emits pulsed laser light, the light-receiving unit 32 outputs information on the number of SPAD elements that detected the incidence of a photon (hereinafter, referred to as "detection number") (for example, a number corresponding to a detection signal described later). For example, the light-receiving unit 32 detects the incidence of a photon at a predetermined sampling period for one light emission of the light source unit 20, and outputs the number of detected photons that have been incident in the same pixel region for each pixel.

[0161] The addition unit 33 adds the number of detected photons output by the light-receiving unit 32 for each of a plurality of SPAD elements (for example, corresponding to one or more pixels), and outputs the added value as a pixel value to the histogram addition processing unit 34 and the ambient light estimation processing unit 35.

[0162] Here, the value of one SPAD element (SPAD value) is 1-bit data having a value {0, 1}. In the addition unit 33, as shown in Figure 2 , a plurality of SPAD pixels 50 that are two-dimensionally arranged are grouped for each p_h x p_w to form one pixel 60, and the sum of the SPAD values in the pixel 60 is represented by a binary number of ceil(log2(p_h p_w)) bits (here, ceil() represents decimal upward rounding) and is used as a pixel value of the pixel.

[0163] As shown in Figure 2 , the addition unit 33 is arranged in parallel for each pixel 60 while calculating the pixel values of all the pixels 60, and outputs the pixel values to the histogram addition processing unit 34 and the ambient light estimation processing unit 35. Figure 2 A two-dimensional SPAD array is shown in which a plurality of SPAD pixels 50 are grouped for each p_h x p_w to form one pixel 60.

[0164] The histogram addition processing unit 34 creates a histogram in which a horizontal axis is a time of flight (for example, a number indicating a sampling order (hereinafter, referred to as "sampling number")) and a vertical axis is a cumulative pixel value based on a pixel value obtained for each of one or more pixels 60. For example, the histogram is created in a memory (not shown) in the histogram addition processing unit 34. The memory can be, for example, a static random access memory (SRAM) or the like. However, the memory is not limited to the SRAM and can be various memories such as a dynamic RAM (DRAM).

[0165] Meanwhile, in addition to the reflected light L2 reflected by the object to be measured and returned, the environmental light L0 reflected and scattered by the object, the atmosphere, or the like is also incident on the light receiving unit 32. The environmental light estimation processing unit 35 estimates the environmental light L0 incident on the light receiving unit 32 together with the reflected light L2 on the basis of an arithmetic mean value of the addition result of the addition unit 33 and provides an environmental light intensity estimate to the histogram addition processing unit 34. The histogram addition processing unit 34 performs a process of subtracting the environmental light intensity estimate value given by the environmental light estimation processing unit 35 and adding the resulting value to the histogram.

[0166] Here, the histogram addition processing is specifically described with reference to FIGS. 3, 4, and 5.

[0167] Figure 3A A histogram of the reflected light of the first laser emission is shown. As shown, the pixel value of the first reflected light is stored in the memory address corresponding to the number of groups of the sampling time. Figure 3B The environmental light intensity estimate value is subtracted and added to the histogram. Figure 3C A histogram of the reflected light of the second laser emission is shown. As shown, the pixel value of the second reflected light is added to the value stored in the memory address corresponding to the number of groups of the sampling time. The environmental light intensity estimate value is subtracted and added to the histogram.

[0168] Figure 4A A histogram of the reflected light of the third laser emission is shown. As shown, the pixel value of the third reflected light is added to the value stored in the memory address corresponding to the number of groups of the sampling time. Figure 4B The environmental light intensity estimate value is subtracted and added to the histogram. Figure 4C

[0169] A histogram of the reflected light of the third laser emission is shown. As shown, the pixel value of the third reflected light is added to the value stored in the memory address corresponding to the number of groups of the sampling time. Figure 5A The environmental light intensity estimate value is subtracted and added to the histogram. Figure 5B Figure 5C

[0170] ​In the histogram of the reflected light generated as described above, the number of groups that capture the reflected light is identified by repeatedly performing a size comparison between the count values of the histogram and a size comparison with a threshold value, such as peak detection.

[0171] The smoothing filter 36 is configured by using, for example, a finite impulse response (FIR; finite length impulse response) filter or the like, to reduce shot noise, reduce the number of unnecessary peaks on the histogram, and perform smoothing processing so as to easily detect the peaks of the reflected light.

[0172] The reflected light detection unit 37 detects the peaks of the mountains by repeatedly performing a size comparison between the count values of adjacent groups of the histogram, obtains the interval of the rising edge of each mountain using a plurality of mountains having large peak values as candidates, and calculates the distance to the object to be measured based on the time of flight of the reflected light. At this time, a plurality of mountains can be detected; however, since the host 40 calculates the final measured distance value with reference to the information of the peripheral pixels, the measured distance values of the plurality of reflected light candidates are transmitted to the host 40 via the external output interface 38.

[0173] The external output interface 38 can be a mobile industry processor interface (MIPI), a serial peripheral interface (SPI), or the like.

[0174] Here, the accumulation of the histogram of the linear representation is described. In the case where the number of accumulations increases, the variance of the ambient light is proportional to the square root of the number of accumulations; however, the reflected light is proportional to the number of accumulations, so that the S / N can be improved.

[0175] The intensity of the reflected light is inversely proportional to the square of the distance; however, the intensity of the ambient light is assumed to be a Gaussian distribution N(μ,σ 2 ), regardless of the distance. Figure 6A An accumulated histogram (accumulated histogram) in the case of one addition is shown. Here, for easy understanding, an example of a case where the reflected light returns to the boxes 5, 100, 200,..., and 900 is shown. Figure 6B An accumulated histogram in the case of four additions is shown, and Figure 7A An accumulated histogram in the case of 16 additions is shown. Figure 7B This is a smoothed histogram after smoothing by the smoothing filter 36 in the case of 16 additions.

[0176] In the case where the change in the intensity of the ambient light is large and the standard deviation is large, it is difficult to distinguish the ambient light from the reflected light. This standard deviation can be used as an indicator of whether the ambient light and the reflected light can be distinguished from each other with high reliability. Figure 8A Random numbers and fixed values of a μ = 50 and σ = 5 normal distribution are shown, and Figure 8BA random number of a normal distribution of μ = 50 and σ = 15 and a fixed value are shown. μ and σ are parameter values of an arithmetic mean and a standard deviation of ambient light used for generating a random number of a normal distribution, respectively.

[0177] As described above, in the light-receiving device 30 serving as a ToF sensor using, for example, a SPAD element as a light-receiving element and performing distance measurement by a ToF method, values of a plurality of SPAD elements are added together to serve as a pixel value; however, in order to capture reflected light by sampling a pixel value after a pulsed laser emission, the pixel value is added to a histogram having a group number corresponding to a sampling time. Reflected light expands two-dimensionally while traveling, and its intensity is inversely proportional to the square of a distance; therefore, by accumulating a histogram of reflected light of a plurality of pulsed laser emissions, S / N is improved by synchronous addition of noise averaging, so that weak reflected light from a farther object to be measured can be discriminated.

[0178] [Problems of Conventional Art]

[0179] However, in a case where a histogram of reflected light is accumulated based on a plurality of laser emissions, a pixel value of strong reflected light from a measurement object to be relatively close is large, and every time a histogram is accumulated, a dynamic range of the histogram increases. Therefore, this increases a capacity of a memory storing a histogram of reflected light based on a plurality of laser emissions. In particular, on a sunny day, ambient light becomes stronger, and most of pixel values become large values; therefore, in order to accumulate more histograms, a bit depth of a histogram count value is required to be more.

[0180] Further, as described above, it is preferable to use a standard deviation to distinguish reflected light and ambient light; however, since a multiplier and a square root arithmetic unit corresponding to a number of pixels are required, this also causes a problem of an increase in circuit size and power consumption. In addition, since data of a histogram is too large, it is difficult to be transmitted to an external device in real time. In order to solve such a problem, a count value of a histogram can be logarithmically transformed, and a result is stored in a memory for the purpose of compressing a dynamic range; however, an inverse transformation of a logarithmically transformed value is required, and logarithmic transformation is performed again after accumulation of a pixel value, which increases power consumption.

[0181] Figure 9A A waveform chart showing a logarithm of accumulation of a histogram of pixel values in a logarithmic representation (indicated by a solid line) of a histogram (indicated by a broken line) of accumulation in the case of the conventional art is shown. Further, Figure 9B A waveform chart showing a logarithm of accumulation of a histogram of values obtained by subtracting an arithmetic mean μ of ambient light (indicated by a broken line) and a logarithmic representation of a histogram of pixel values of a logarithm of accumulation of values obtained by subtracting an arithmetic mean μ of ambient light (indicated by a solid line) in the case of the conventional art is shown.

[0182] <First embodiment of the present invention>

[0183] In the technology according to the present disclosure, in a light-receiving device including a light-receiving unit having a plurality of light-receiving elements (for example, SPAD elements), and based on reflected light from an object to be measured received by pulsed light applied by a light source unit, and a distance measuring device including the light-receiving device, the plurality of SPAD elements are added together in a predetermined time to be used as a pixel value D, and the pixel value D is converted into a logarithmic value or an approximate value thereof to obtain logarithmic representation data LogD.

[0184] A histogram of the accumulated pixel values in the logarithmic representation is equivalent to calculating an amount proportional to the geometric mean value. By using this, the logarithmic conversion is performed on the pixel value D and the calculation is performed as it is. That is, the signal processing after the logarithmic conversion in the logarithmic representation is performed, and the distance measurement for measuring the distance d to the object to be measured 10 is performed.

[0185] In the signal processing after the logarithmic conversion, the dynamic range of the histogram can be compressed by accumulating the histogram of the pixel values in the logarithmic representation, which can reduce the memory capacity. Further, in the signal processing after the logarithmic conversion, the arithmetic processing is simplified by using the fact that the arithmetic mean value in the logarithmic representation is equal to the logarithmic representation of the geometric mean value.

[0186] Figure 10 A waveform chart showing the logarithm of the accumulation of the histogram of the logarithmic representation of the pixel values (indicated by a solid line) and the logarithm of the accumulation of the histogram of the logarithmic representation of the pixel values (indicated by a broken line) is shown. Further, Figure 11 A waveform chart showing the logarithm of the accumulation of the histogram of the values obtained by subtracting the arithmetic mean value μ of the ambient light (indicated by a broken line) and the logarithm of the accumulation of the histogram of the logarithmic representation of the pixel values obtained by subtracting the arithmetic mean value μ of the ambient light (indicated by a solid line) is shown.

[0187] Hereinafter, a specific example of a light-receiving device and a distance measuring device according to the first embodiment of the present disclosure will be described. The distance measuring device according to the first embodiment is a so-called flash-type distance measuring device in which pixels including SPAD elements are two-dimensionally arranged in a matrix and a wide-angle distance measurement image is acquired at one time.

[0188] <<Example 1>>

[0189] Example 1 is an example in which logarithmic representation data is obtained after subtracting a predetermined value M from the pixel value D. For example, as the predetermined value M, the arithmetic mean value μ of the ambient light can be exemplified. Figure 12 is a block diagram showing a configuration example of the light-receiving device and the distance measuring device of Example 1 according to the first embodiment of the present disclosure.

[0190] In Example 1, a value (D-M) obtained by subtracting a predetermined value M from a pixel value D is converted into a logarithmic value or an approximation thereof to obtain logarithmic representation data Log(D-M). Then, the logarithmic representation data Log(D-M) is stored and calculated to perform distance measurement. However, in a case where D < M, the conversion into the logarithmic value or the approximation thereof is performed with D-M as 0.

[0191] LogD = log2(1 + Max(D-M, 0))

[0192] Here, the flow of a signal processing method (the signal processing method of the present disclosure) in the light receiving apparatus according to Example 1 is described with reference to the flowchart of Figure 13 Fig. 1. For example, it is assumed that the signal processing is performed under the control of a control unit 31 implemented by an information processing device (for example, a CPU).

[0193] The control unit 31 acquires the pixel value D from the addition unit 33 (step Sll), then subtracts the predetermined value M from the pixel value D (step S12), and converts the subtraction result (D-M) into a logarithmic value or an approximation thereof to obtain the logarithmic representation data Log(D-M) (step S13). Next, the control unit 31 stores and calculates the logarithmic representation data Log(D-M) (step S14), and then performs distance measurement using the ToF method to measure the distance d to the object to be measured 10 (step S15).

[0194] Here, the predetermined value M is an ambient light intensity estimate (AMP-U + OFFSET) obtained by multiplying a statistical value U by a predetermined multiplier AMP and adding a predetermined addend OFFSET to the result. The statistical value U can be an arithmetic mean value of the pixel values in the ambient light collection period, a geometric mean value of the pixel values, a maximum value of the pixel values, a minimum value of the pixel values, a median value of the pixel values, or the like. In Example 1, only the arithmetic mean value and the geometric mean value are exemplified; however, the maximum value, the minimum value, the median value, or the like can be used to calculate the statistical value in a similar period in a similar part. Further, another configuration is possible in which, in a case where the predetermined multiplier AMP is 1 and the predetermined addend OFFSET is 0, the statistical value U itself is used as the predetermined value M.

[0195] [Configuration Example of System]

[0196] The distance measurement apparatus 1 according to Example 1 includes a light source unit 20 that applies light to an object 10 to be measured, a light receiving apparatus 30 that receives reflected light from the object to be measured 10 based on the pulsed light applied by the light source unit 20, and a host 40. The light source unit 20 includes, for example, a laser light source that emits laser light having a peak wavelength in an infrared wavelength region.

[0197] The light-receiving device 30 is a ToF sensor that uses a ToF method as a measurement method for measuring the distance d from the object to be measured 10, and includes, in addition to the control unit 31, the light-receiving unit 32, the addition unit 33, and the external output interface 38, a logarithmic conversion processing unit 61, a logarithmically represented ambient light estimation processing unit 62, a logarithmically represented histogram addition processing unit 63, a logarithmically represented smoothing filter 64, a logarithmic conversion unit 65, and a logarithmically represented reflected light detection unit 66.

[0198] [Exemplary Configuration Example of Light-Receiving Unit]

[0199] Figure 14 is a block diagram showing an exemplary configuration example of the light-receiving unit 32 in the light-receiving device 30 according to Example 1. The exemplary configuration example of the light-receiving unit 32 is similar in each of the examples described later.

[0200] As shown in Figure 2 , the light-receiving unit 32 includes a timing control circuit 321, a drive unit 322, a SPAD array unit 323, and an output unit 324.

[0201] The SPAD array unit 323 includes a plurality of SPAD pixels 50 arranged in a matrix in two dimensions. A pixel drive line LD (row direction in the drawing) is connected to the plurality of SPAD pixels 50 for each pixel row, and an output signal line LS (column direction in the drawing) is connected to the plurality of SPAD pixels 50 for each pixel column. One end of the pixel drive line LD is connected to an output end corresponding to each row of the drive unit 322, and one end of the output signal line LS is connected to an input end corresponding to each column of the output unit 324.

[0202] The drive unit 322 includes a shift register and an address decoder, and drives each pixel 50 of the SPAD array unit 323 at the same time for all pixels in units of pixel columns and the like. Specifically, the drive unit 322 includes at least a quenching voltage V QCH applied to each pixel 50 in a selected column in the SPAD array unit 323 and a selection control voltage V SEL applied to each pixel 50 in the selected column. Then, the drive circuit 322 applies the selection control voltage V SEL to the pixel drive line LD corresponding to the pixel column to be read out; thereby selecting the SPAD pixel 50 for detecting the incidence of a photon in units of pixel columns.

[0203] The signal (hereinafter, referred to as “detection signal”) V OUTis supplied to the output unit 324 through each of the output signal lines LS. The output unit 324 outputs the detection signal V OUT to the addition unit 33 (see Figure 13 ).

[0204] The timing control unit 321 includes a timing generator that generates various timing signals and the like, and controls the drive unit 322 and the output unit 324 on the basis of the various timing signals generated by the timing generator.

[0205] (Schematic configuration example of SPAD array unit)

[0206] Figure 15 is a schematic diagram illustrating a schematic configuration example of the SPAD array unit 323 in the light-receiving unit 32 of the light-receiving device 30 according to Example 1. The schematic configuration example of the SPAD array unit 323 is similar in each of the examples described later.

[0207] As illustrated in Figure 15 , the SPAD array unit 323 includes a plurality of SPAD pixels 50 arranged in a matrix two-dimensionally, for example. The plurality of SPAD pixels 50 are grouped into a plurality of pixels 60 constituted by a predetermined number of SPAD pixels 50 arranged in a row direction and / or a column direction. The shape of an area connected by outer edges of the SPAD pixels 50 located at the outermost periphery of each pixel 60 is a predetermined shape (for example, a rectangular shape). The shape can be a two-dimensional arrangement in units of pixels, in which pixels are arranged in a row direction, and in this case, a row is selected and read out in units of rows.

[0208] (Circuit configuration example of SPAD pixel)

[0209] Figure 16 is a circuit diagram illustrating a circuit configuration example of the pixel 50 in the SPAD array unit 323 of the light-receiving device 30 according to Example 1. The schematic configuration example of the circuit configuration example of the SPAD pixel 50 is similar in each of the examples described later.

[0210] As illustrated in Figure 16 , the SPAD pixel 50 includes a SPAD element 51 as an example of a light-receiving element and a readout circuit 52 that detects the incidence of a photon on the SPAD element 51. When a photon is incident in a state in which a reverse bias voltage V SPAD equal to or higher than a breakdown voltage is applied between an anode electrode and a cathode electrode, the SPAD element 51 generates an avalanche current.

[0211] The readout circuit 52 includes a quenching resistor 53 , a selection transistor 54 , a digital converter 55 , an inverter 56 , and a buffer 57 .

[0212] For example, the quenching resistor 53 is an N-type metal oxide semiconductor field effect transistor (MOSFET). (hereinafter referred to as "NMOS transistor"). The NMOS transistor constituting the quenching resistor 53 has a drain electrode connected to the anode electrode of the SPAD element 51 and a source electrode connected to the ground via the selection transistor 54. In addition, the quenching resistor 53 is connected to the anode electrode of the SPAD element 51 via the pixel drive line LD. Figure 14 The driving unit 322 in the circuit applies a preset quenching voltage V to the gate electrode of the NMOS transistor for causing the NMOS transistor constituting the quenching resistor 53 to function as a quenching resistor. QCH .

[0213] The SPAD element 51 is an avalanche photodiode that operates in a Geiger mode in response to a reverse bias voltage equal to or higher than a breakdown voltage applied between an anode electrode and a cathode electrode and can detect incidence of one photon.

[0214] The selection transistor 54 is composed of, for example, an NMOS transistor, the drain electrode of which is connected to the source electrode of the NMOS transistor constituting the quenching resistor 53, and the source electrode of which is grounded. SEL Through the pixel drive line LD from Figure 14 When the driving unit 322 is applied to the gate electrode of the selection transistor 54, the selection transistor 54 changes from the off state to the on state.

[0215] The digital converter 55 includes a resistor element 551 and an NMOS transistor 552. The NMOS transistor 552 has a voltage connected to the power supply voltage V via the resistor element 551. DD The drain electrode of the NMOS transistor 552 is connected to the node of the SPAD element 51 and has a source electrode connected to the ground. In addition, the gate electrode of the NMOS transistor 552 is connected to the connection node N1 between the anode electrode of the SPAD element 51 and the quenching resistor 53.

[0216] The inverter 56 has a configuration of a CMOS inverter including a P-type MOSFET (hereinafter, referred to as a "PMOS transistor") 561 and an NMOS transistor 562. The drain of the PMOS transistor 561 is connected to a power supply voltage V DDThe source of the PMOS transistor 561 is connected to the drain of the NMOS transistor 562. The drain electrode of the NMOS transistor 562 is connected to the source electrode of the PMOS transistor 561, and the source electrode is grounded. The gate electrode of the PMOS transistor 561 and the gate electrode of the NMOS transistor 562 are commonly connected to the connection node N2 between the resistor element 551 and the drain electrode of the NMOS transistor 552. The output terminal of the inverter 56 is connected to the input terminal of the buffer 57.

[0217] The buffer 57 is a circuit for impedance conversion, and the buffer 57 converts the impedance of the output signal thus input in response to the output signal input from the inverter 56, and outputs the result as a detection signal V OUT .

[0218] (Schematic operation example of a SPAD pixel)

[0219] For example, Figure 16 The readout circuit 52 shown in FIG operates as follows. That is, first, when the control voltage V is selected, SEL from Figure 14 During the period when the driving unit 322 is applied to the gate electrode of the selection transistor 54 and the selection transistor 24 is in the on state, a reverse bias voltage V that is equal to or higher than the breakdown voltage is applied. SPAD is applied to the SPAD element 51. Thus, the operation of the SPAD element 51 is enabled.

[0220] On the other hand, when selecting the control voltage V SEL No from Figure 14 During the period when the driving unit 322 is applied to the selection transistor 54 and the selection transistor 54 is in the off state, the reverse bias voltage V SPAD is not applied to the SPAD element 51. Therefore, the operation of the SPAD element 51 is disabled.

[0221] When a photon is incident on the SPAD element 51 while the selection transistor 54 is in the on state, an avalanche current is generated in the SPAD element 51. Therefore, the avalanche current flows through the quenching resistor 53 to increase the voltage of the connection node N1. Then, if the voltage of the connection node N1 becomes higher than the turn-on voltage of the NMOS transistor 552, the NMOS transistor 552 is turned on, and the voltage of the connection node N2 increases from the power supply voltage V DD becomes 0V.

[0222] Then, if the voltage of the connection node N2 is increased from the power supply voltage V DD becomes 0V, the PMOS transistor 561 changes from the off state to the on state, the NMOS transistor 562 changes from the on state to the off state, and the voltage of the connection node N3 changes from 0V to the power supply voltage V DDAs a result, a high-level detection signal V is output from the buffer 77. OUT .

[0223] Thereafter, if the voltage of the connection node N1 continues to increase, the voltage applied between the anode electrode and the cathode electrode of the SPAD element 51 becomes less than the breakdown voltage. This stops the avalanche current to reduce the voltage of the connection node N1. Then, if the voltage of the connection point N1 becomes lower than the turn-on voltage of the NMOS transistor 552, the NMOS transistor 552 is turned off, and the detection signal V from the buffer 57 is stopped. OUT That is, the detection signal V OUT becomes low level.

[0224] As described above, the readout circuit 52 outputs the high-level detection signal V during the period from the timing when a photon enters the SPAD element 51 to generate an avalanche current and then turn on the NMOS transistor 552 to the timing when the avalanche current stops to turn off the NMOS transistor 552. OUT .

[0225] The detection signal V output from the readout circuit 52 OUT via Figure 14 The output unit 324 in the input is input to the adding unit 33 of each pixel 60 (see Figure 14 ). Therefore, for each pixel 60, the detection signal V is the number of SPAD pixels 50 (detection number) that detect the incidence of photons among the plurality of SPAD pixels 50 constituting one pixel 60. OUT It is input to the adding unit 33.

[0226] [Configuration example of adding unit]

[0227] Figure 17 : is a block diagram showing a configuration example of the adding unit 33 in the light receiving device 30 according to Example 1. Figure 17 As shown, the adding unit 33 includes, for example, a pulse shaping unit 331 and a light reception number counting unit 332. In each example described later, the configuration example of the adding unit 33 is similar.

[0228] The pulse shaping unit 331 generates the pulse from the output unit 324 according to the working clock of the adding unit 33. Figure 14 The detection signal V supplied to the SPAD array unit 322 shown in FIG. OUT The pulse waveform is shaped into a pulse waveform with a time width.

[0229] The light reception number counting unit 332 counts the detection signal V input from the corresponding pixel 60 for each sampling period. OUTThe count is performed; thus, the number of pixels 50 in which the incidence of photons is detected (the number of detections) is counted for each sampling period, and the count value is output as the pixel value D of the pixel 60.

[0230] Note that, in the pixel value D [i] [8: 0] in Figure 17 [i] is an identifier for identifying each SPAD pixel 50, and is a value from “0” to “R-1” in this example (see Figure 15 ). Further, [8: 0] indicates the bit depth of the pixel value D [i].

[0231] Figure 17 It is shown that the addition unit 33 generates a 9-bit pixel value D that can take values “0” to “511” based on the detection signal V OUT input from the pixel 60 identified by the identifier i.

[0232] Here, the sampling period is a period that measures the time (time of flight) from when the laser light L1 is emitted from the light source unit 20 to when the incidence of photons is detected by the light receiving unit 32 of the light receiving device 30. As the sampling period, a period shorter than the light emission period of the light source unit 20 is set. For example, the sampling period is further shortened, which makes it possible to estimate or calculate the time of flight of the photons emitted from the light source unit 20 and reflected by the object to be measured 10 with higher time resolution. This means that the distance to the object 90 can be estimated or calculated with higher distance measurement resolution by increasing the sampling frequency.

[0233] For example, assuming that the time of flight from when the light source unit 20 emits the laser light L1 to when the laser light L1 is reflected by the object to be measured 10 and the reflected light L2 enters the light receiving unit 32 is denoted by t, since the speed of light C is constant (C ≈ 300 million m / s), the distance d to the object to be measured 10 can be estimated or calculated according to the above equation (d = C × (t / 2)).

[0234] In view of this, assuming that the sampling frequency is 1 GHz, the sampling period is 1 nanosecond. In this case, one sampling period corresponds to 15 cm. This indicates that the distance measurement resolution is 15 cm for the case where the sampling frequency is set to 1 GHz. Further, assuming that the sampling frequency is 2 gigahertz, which is twice 1 gigahertz, the sampling period is 0.5 nanoseconds, and thus one sampling period corresponds to 7.5 cm. This indicates that for the case where the sampling frequency is doubled, the distance measurement resolution can be reduced to 1 / 2. As described above, by increasing the sampling frequency and shortening the sampling period, the distance to the object to be measured 10 can be estimated or calculated more accurately.

[0235] [Configuration example of logarithmic transformation processing unit]

[0236] Figure 18is a block diagram showing a configuration example of the log conversion processing unit 61 in the light receiving device 30 according to Example 1.

[0237] The log conversion processing unit 61 receives an input of the pixel value D from the addition unit 33 via a D flip-flop (FF) 71. The D flip-flop 71 is enabled during a period in which the histogram is updated and during a period in which the ambient light intensity estimate as the predetermined value M is acquired.

[0238] As shown in Figure 18 The log conversion processing unit 61 includes a subtracter 611, a clip circuit 612, a log conversion unit 613, a selector 614, a log / linear representation setting unit 615, and a D flip-flop 616.

[0239] The subtracter 611 subtracts the predetermined value M (estimated ambient light intensity estimate) from the pixel value D input from the addition unit 33 in the ambient light estimate processing unit 62 in the log representation. The subtraction result (D-M) of the subtracter 611 is supplied to the log conversion unit 613 via the clip circuit 612 and used as one input of the selector 614.

[0240] The log conversion unit 613 converts the subtraction result (D-M) obtained by subtracting the predetermined value M from the pixel value D into a log value or an approximate value of the log value to obtain log representation data Log(D-M). However, in the case of D < M, the conversion of the log value or the approximate value thereof is performed with D-M as 0. The log representation data Log(D-M) is used as the other input of the selector 614.

[0241] The selector 614 selects one of the two inputs based on setting information lsel from the log / linear representation setting unit 615. The log / linear representation setting unit 615 outputs the setting information lsel of logical "0" in the log representation and logical "1" in the linear representation.

[0242] Accordingly, the selector 614 selects the log representation data Log(D-M) of the linear representation or the pixel value D based on the setting information lsel. That is, the light receiving device 30 including the log conversion processing unit 61 according to this example has a mode of performing distance measurement by processing (storing and calculating) the log representation data LogD obtained by converting the pixel value D into a log value or an approximate value thereof, and a mode of performing distance measurement by processing (storing and calculating) the pixel value as the linear representation, and the light receiving device 30 is configured to switch between the modes.

[0243] The log representation data Log(D-M) of the linear representation or the pixel value D selected by the selector 614 is supplied to the next stage histogram addition processing unit 63 of the log representation via the D flip-flop 616. The D flip-flop 616 is enabled during a period in which the histogram is updated.

[0244] [Configuration example of the log-expressed ambient light estimation processing unit]

[0245] Figure 19 is a block diagram showing a configuration example of the log-expressed ambient light estimation processing unit 62 in the light receiving device 30 according to Example 1. Note that the log-expressed ambient light estimation processing unit 62 is not an essential constituent element of the light receiving device 30 according to Example 1. That is, the log-expressed ambient light estimation processing unit 62 can be omitted without subtracting the predetermined value M (ambient light intensity estimate) from the pixel value D.

[0246] The log-expressed ambient light estimation processing unit 62 receives an input of the pixel value D from the addition unit 33 via a D flip-flop 71. The D flip-flop 71 is enabled during a period in which the histogram is updated and during a period in which the ambient light intensity estimate is acquired.

[0247] As shown in Figure 19 , the log-expressed ambient light estimation processing unit 62 includes a logarithmic conversion unit 6201, a selector 6202, an arithmetic / geometric mean value setting unit 6203, an adder 6204, a D flip-flop 6205, a divider 6206, and a D flip-flop 6207. The log-expressed ambient light estimation processing unit 62 further includes a selector 6208, a parameter setting unit 6209, an adder 6210, a parameter setting unit 6211, a D flip-flop 6212, an inverse conversion unit 6213, a 1-bit left shift circuit 6214, and a selector 6215.

[0248] The pixel value D input from the addition unit 33 is converted into a logarithmic value or an approximate value thereof by the logarithmic conversion unit 6201, and is used as one input of the selector 6202 and directly as the other input of the selector 6202.

[0249] The selector 6202 selects one of the two inputs based on the setting information msel from the arithmetic / geometric mean value setting unit 6203. The arithmetic / geometric mean value setting unit 6203 outputs the setting information msel of which the arithmetic mean value is logical "0" and the geometric mean value is logical "1". By this, the selector 6202 selects the pixel value D or the log-expressed data LogD based on the setting information msel.

[0250] The pixel value D or the log-expressed data LogD selected by the selector 6202 is input to the adder 6204. The adder 6204 adds the pixel value D or the log-expressed data LogD to the latched data of the D flip-flop 6205 of the next stage. The D flip-flop 6205 is enabled only during a measurement period of a statistical value of the ambient light.

[0251] The divider 6206 obtains a statistical value of the ambient light by dividing the latch data of the D flip-flop 6205 by the number N of data. The D flip-flop 6207 enables only one cycle at the end of each measurement period of the statistical value of the ambient light, and latches the statistical value of the ambient light, which is a geometric mean or an arithmetic mean obtained by the divider 6206.

[0252] The statistical value U that is the geometric mean or the arithmetic mean latched by the D flip-flop 6207 is another input of the selector 6208 having 0 as one input. The selector 6208 selects one of the two inputs based on a predetermined multiplier AMP set by the parameter setting unit 6209, and uses the selected input as an input of the adder 6210. The adder 6210 repeats an addition process of the data selected by the selector 6208 and the output data of the 1-bit shift circuit 6214 based on a predetermined addend OFFSET set by the parameter setting unit 6211, the same number of times as the bit depth of the multiplier AMP.

[0253] After the measurement period of the statistical value of the ambient light ends and the statistical value U is latched, the D flip-flop 6212 enables for the same period as the bit depths of the multiplier AMP and the addend OFFSET, and calculates AMP x U + OFFSET. Figure 20 An explanatory diagram of the calculation process in the ambient light estimation processing unit 62, that is, the calculation process of AMP x U + OFFSET, is shown in logarithmic representation.

[0254] The latched data of the D flip-flop 6212 is inverse-transformed (subjected to inverse logarithmic transformation) by the inverse transformation unit 6213 to become one input of the selector 6215 and directly become another input of the selector 6215.

[0255] The selector 6215 selects one of the two inputs based on the setting information msel from the arithmetic / geometric mean setting unit 6203. Specifically, when the setting information msel is logical "0", the selector 6215 selects the latched data of the D flip-flop 6212, and when the setting information msel is logical "1", the selector 6215 selects the output data of the inverse transformation unit 6213, and outputs the selected output data to the logarithmic transformation processing unit 61.

[0256] [Configuration example of histogram addition processing unit in logarithmic representation]

[0257] The histogram addition processing unit 63 correlates the time of flight from emission of laser light from the light source unit 20 to return of reflected light as a bin of a histogram, and stores logarithmic representation data calculated based on pixel values sampled at each time in a memory as a count value of the bin corresponding to the time.

[0258] Assuming regarding the histogram addition processing unit 63, the histogram is updated by adding the logarithmic representation data Log(D-M) based on each of the reflection light from the object to be measured by the laser emission performed multiple times to the count value of the bin corresponding to the time. Then, the distance measurement calculation is performed using the histogram obtained by accumulating the count value calculated based on the pixel value obtained by receiving the reflection light based on the laser emission performed multiple times.

[0259] With this configuration, it is possible to reduce the bit depth of the memory storing the histogram or to expand the dynamic range of the histogram at the time of accumulation. Furthermore, it is possible to calculate the logarithmic value of the geometric mean. The execution of the quantization of the number reduces the variation due to large noise. Hereinafter, the configuration of the histogram addition processing unit 63 is described specifically.

[0260] Figure 21 is a block diagram showing a configuration example of the logarithmic representation histogram addition processing unit 63 in the light receiving device 30 according to Example 1. As shown in Figure 21 the histogram addition processing unit 63 includes an adder 631, a D flip-flop 632, an SRAM 633, a D flip-flop 634, an adder (+1) 635, a D flip-flop 636, and a D flip-flop 637.

[0261] Here, the SRAM 633 inputting the read address READ_ADDR (RA) and the SRAM 633 inputting the write address WRITE_ADDR (WA) are the same SRAM (memory). The latter SRAM 633 is enabled during the period in which the histogram is updated.

[0262] The histogram addition processing unit 63 receives the input of the logarithmic representation data Log(D-M) or the linear representation pixel value D from the logarithmic conversion processing unit 61. The adder 631 adds the read data READ_DATA (RD) from the SRAM 633 to the input of the logarithmic representation data Log(D-M) or the linear representation pixel value D.

[0263] The D flip-flop 632 is enabled during the period in which the histogram is updated, and latches the addition result of the adder 631. Then, the D flip-flop 632 supplies the latched data to the SRAM 633, and the write address WA is inputted to the SRAM 633 as the write data WRITE_DATA (WD).

[0264] The D flip-flop 632 is enabled during the period in which the histogram is updated and the period in which the histogram data HIST_DATA is transferred. The D flip-flop 632 then supplies the latched data to the SRAM 633 as the read address READ_ADDR. The adder 634 increases the bin number (BIN) by adding 1 to the latched data of the D flip-flop 632.

[0265] The read data READ_DATA read out from the SRAM 633 is output as the histogram data HIST_DATA. The D flip-flop 636 is enabled during the period in which the histogram is updated, and latches the latched data of the D flip-flop 634. During the period in which the histogram is updated, the D flip-flop 637 is enabled, and latches the latched data of the D flip-flop 636. The latched data of the D flip-flop 637 is output as the histogram bin number HIST_BIN.

[0266] Figure 22 is an explanatory diagram of the logarithmic transformation and the inverse transformation. The logarithmic transformation and the exponential transformation are performed using a broken line approximation. In a case where a logarithmic representation is represented by a fixed point number u3.3 (u is a minimum unit of a rounding error) and a linear representation of an inverse transformation is represented by a fixed point number u8.0, it can be simply implemented like Figure 23 the hardware language Verilog HDL code shown in

[0267] log21+x: u8.0 → u3.3 (LOG2)

[0268] 2 x -1: u3.3 → u8.0 (EXP2)

[0269] The description returns Figure 13 In Figure 13 , the smoothing filter 64 performs a smoothing process of the logarithmic representation of the cumulative histogram output from the histogram addition processing unit 63. Specifically, the smoothing filter 64 reduces the amount of peak values on the histogram, and performs a smoothing process so that it is easy to detect the peak value of the reflected light.

[0270] The logarithmic transformation unit 65 further logarithmically transforms and compresses the logarithmic representation of the cumulative histogram smoothed by the smoothing filter 64. Details of the process of the logarithmic transformation unit 65 are described later.

[0271] The reflected light detection unit 66 detects the peak of the mountain by repeating a size comparison between the count values of the adjacent bin numbers of the logarithmic representation of the histogram. Then, using a plurality of mountains having large peak values as candidates, an interval of the rising edge of each mountain is obtained, and a distance to the object under test is calculated based on the time of flight of the reflected light.

[0272] Further, the reflected light detection unit 66 compares the size between the count value of the histogram and a value obtained from the logarithmic representation by the inverse logarithmic transformation (transforming into an exponential function, returning a value of a linear representation by a square power, or an approximate value thereof), to detect the peak value of each reflected light. Then, a distance can be calculated based on the time corresponding to the bin number at which the peak value starts to rise.

[0273] Figure 24AThe output waveform of the addition 33 is shown, Figure 24B The output waveform of the logarithmic conversion processing unit 61 is shown, Figure 25A The output waveform of the histogram addition processing unit 63 in the logarithmic representation is shown, Figure 25B The output waveform of the smoothing filter 64 in the logarithmic representation is shown, and Figure 26 The output waveform of the logarithmic conversion unit 65 is shown.

[0274] Here, for the case where the predetermined value M is not subtracted from the pixel value D (i.e., the case where the ambient light intensity estimate is an arithmetic average), the accumulation of the histogram of the pixel value in the logarithmic representation is described, and for the case where the predetermined value M is subtracted from the pixel value D, the accumulation of the histogram of the pixel value in the logarithmic representation is described.

[0275] (Arithmetic average of ambient light is not subtracted from the pixel value D)

[0276] Figure 27A The accumulated histogram in the case of one addition is shown, Figure 27B The accumulated histogram in the case of four additions is shown, and Figure 28A The accumulated histogram in the case of 16 additions is shown. Further, Figure 28B The smoothed histogram after smoothing by the smoothing filter 64 in the logarithmic representation in the case of 16 additions is shown.

[0277] (Arithmetic average of ambient light is subtracted from the pixel value D)

[0278] Figure 29A The accumulated histogram in the case of one addition is shown, Figure 29B The accumulated histogram in the case of four additions is shown, Figure 30A The accumulated histogram in the case of 16 additions is shown. Further, Figure 30B The smoothed histogram after smoothing by the smoothing filter 64 in the logarithmic representation in the case of 16 additions is shown.

[0279] <<Embodiment 2>>

[0280] Example 2 is an example of obtaining the logarithmic representation data by converting the pixel value D into a logarithmic value or an approximate value thereof, and then subtracting the predetermined value M in the logarithmic representation Figure 31 is a block diagram showing a configuration example of the light-receiving device and the distance measuring device according to Example 2 of the first embodiment of the present disclosure.

[0281] In Example 2, the value is obtained by subtracting log representation data LogM obtained by transforming a predetermined value M (for example, the arithmetic mean value of the ambient light) into a logarithmic value or an approximate value thereof from log representation data LogD2 obtained by transforming the pixel value D into a logarithmic value or an approximate value thereof. This means that the normalized logarithm is calculated so that M is calculated as 1. Then, the log representation data LogD (= LogD2 - LogM) is stored and calculated for distance measurement.

[0282] LogD2 = log2(1 + D2)

[0283] LogM = log2(1 + M)

[0284] LogD = log2(1 + D2) - log2(1 + M)

[0285] [Configuration example of system]

[0286] The distance measurement device 1 according to Example 2 further includes a light source unit 20 that applies light to the object to be measured (object) 10, a light receiving device 30 that receives reflected light from the object to be measured 10 based on the pulsed light applied by the light source unit 20, and a host computer 40.

[0287] For the light receiving device 30 that is a ToF sensor employing the ToF method, in Example 1, the log representation ambient light estimation processing unit 62 is arranged in parallel with the log transformation processing unit 61, and performs log transformation after subtracting a predetermined value M (for example, the arithmetic mean value of the ambient light) from the pixel value D, while in Example 2, the geometric mean value-based ambient light estimation processing unit 67 is arranged at a later stage of the log transformation processing unit 61.

[0288] The log transformation processing unit 61 generates log representation data LogD2 obtained by transforming the pixel value D input from the addition unit 33 into a logarithmic value or an approximate value thereof. The geometric mean value-based ambient light estimation processing unit 67 generates log representation data LogM obtained by transforming a predetermined value M (for example, the arithmetic mean value of the ambient light) into a logarithmic value or an approximate value thereof. Then, the log representation histogram addition processing unit 63 generates log representation data LogD (= LogD2 - LogM) by subtracting the log representation data LogM from the log representation data LogD2.

[0289] The configuration other than the log transformation processing unit 61, the geometric mean value-based ambient light estimation processing unit 67, and the log representation histogram addition processing unit 63 is the same as in the case of Example 1. In Example 2, since subtraction (LogD2 - LogM) is performed in log representation and division is performed when returning to linear, normalization is performed so that the arithmetic mean value of the ambient light becomes 1.

[0290] Considering only the reduction of the input range by the logarithmic compression, it is expected that the function and effect of the processing of the subsequent stage are similar to those in the case of Example 1. However, in the case of Example 2, the bit depth of the fractional part of the fixed-point number representation of the logarithmic transformation and the inverse transformation requires more than in the case of Example 1.

[0291] [Configuration example of logarithmic transformation processing unit]

[0292] Figure 32A is a block diagram showing a configuration example of the logarithmic transformation processing unit 61 in the light-receiving device 30 according to Example 2.

[0293] In the light-receiving device 30 according to Example 2, since the logarithmic transformation processing unit 61 does not perform the processing of subtracting the predetermined value M from the pixel value D, the logarithmic transformation processing unit 61 does not include the subtracter 611 and the clipper circuit 612 in Figure 18 ; however, as shown in Figure 32A , it includes the logarithmic transformation unit 613, the selector 614, the logarithmic / linear representation setting unit 615, and the D flip-flop 616.

[0294] The functions and the like of the logarithmic transformation unit 613, the selector 614, the logarithmic / linear representation setting unit 615, and the D flip-flop 616 are basically the same as those in the case of Example 1. The D flip-flop 616 is enabled during the period in which the histogram is updated, latches the logarithmic representation data LogD or the pixel value D of the linear representation selected by the selector 614, and outputs the latched data (LogD or D) as the output of the logarithmic transformation processing unit 61.

[0295] [Configuration example of ambient light estimation processing unit based on geometric mean]

[0296] Figure 32B is a block diagram showing a configuration example of the ambient light estimation processing unit 67 based on the geometric mean in the light-receiving device 30 according to Example 2. Note that the logarithmic representation ambient light estimation processing unit 62 is not a necessary constituent element of the light-receiving device 30 according to Example 2. That is, in the case where the ambient light intensity estimation is not subtracted from the pixel value D, the logarithmic representation ambient light estimation processing unit 62 can be omitted.

[0297] As shown in Figure 32B , the ambient light estimation processing unit 67 based on the geometric mean in the light-receiving device 30 according to Example 2 includes the adder 6204, the D flip-flop 6205, the divider 6206, and the D flip-flop 6207. The ambient light estimation processing unit 67 further includes the selector 6208, the parameter setting unit 6209, the adder 6210, the parameter setting unit 6211, the D flip-flop 6212, and the 1-bit left shift circuit 6214.

[0298] The ambient light estimation processing unit 67 receives an input of the pixel value D or the logarithmic representation data LogD from the logarithmic conversion processing unit 61. The adder 6204 adds the pixel value D or the logarithmic representation data LogD input from the logarithmic conversion processing unit 61 to the latched data of the D flip-flop 6205 of the next stage. The D flip-flop 6205 is enabled only during the measurement period of the statistical value of the ambient light.

[0299] The divider 6206 obtains the statistical value of the ambient light by dividing the latched data of the D flip-flop 6205 by the number N of data. After the measurement period of the statistical value of the ambient light is completed, the D flip-flop 6207 is enabled only for one period, and latches the statistical value of the ambient light obtained by the divider 6206. The statistical value of the ambient light, which is the output of the D flip-flop 6207, is the logarithm of the geometric mean at the time of the previous (1-1st) histogram addition. The selector 6208 and the subsequent components are selected so as to be substantially similar to the case of the ambient light estimation processing unit 62 shown in FIG. 6B. Figure 19

[0300] [Configuration example of histogram addition processing unit in logarithmic representation]

[0301] Figure 33 is a block diagram showing a configuration example of the histogram addition processing unit 63 of the logarithmic representation in the light-receiving device 30 according to Example 2.

[0302] In the light-receiving device 30 according to Example 2, since the histogram addition processing unit 63 of the logarithmic representation performs the subtraction processing of the ambient light intensity estimation, the histogram addition processing unit 63 includes a subtracter 638 and a clipper circuit 639 in addition to the constituent elements of the histogram addition processing unit 63 of Example 1.

[0303] Here, the SRAM 633 which inputs the read address READ_ADDR (RA) and the SRAM 633 which inputs the write address WRITE_ADDR (WA) are the same SRAM (memory). The latter SRAM 633 is enabled during the period in which the histogram is updated.

[0304] The histogram addition processing unit 63 receives an input of the logarithmic representation data LogD or the linear representation pixel value D from the logarithmic conversion processing unit 61. The adder 631 adds the read data READ_DATA (RD) from the SRAM 633 to the input logarithmic representation data LogD or the input linear representation pixel value D.

[0305] ​The subtracter 638 subtracts the ambient light intensity estimate estimated by the ambient light estimation processing unit 67 from the addition result of the adder 631. The subtraction result of the subtracter 638 is supplied to the D flip-flop 632 via the clip circuit 639. The D flip-flop 632 is enabled only for one cycle at the end of each measurement period of the statistical value of the ambient light, and latches the value obtained by subtracting the ambient light intensity estimate from the logarithmic representation of the pixel value. The value obtained by subtracting the ambient light intensity estimate from the logarithmic representation of the pixel value is the logarithmic representation of the value obtained by normalizing the pixel value by the geometric mean, and is supplied as the write data WRITE_DATA (WD) to the SRAM 633 to which the write address WA is input.

[0306] The functions and operations of the other constituent elements, that is, the SRAM 633, the D flip-flop 634, the adder 635, the D flip-flop 636, and the D flip-flop 637, are basically the same as those in the case of Example 1.

[0307] <<Example 3>>

[0308] Example 3 is an example in which an arithmetic mean and a variance of an ambient light estimation process are calculated in a logarithmic representation. Figure 34 is a block diagram showing a configuration example of a light-receiving device and a distance measuring device according to Example 3 of the first embodiment of the present disclosure.

[0309] [Configuration example of system]

[0310] The distance measuring device 1 according to Example 3 further includes a light source unit 20 that applies light to the object to be measured (object) 10, a light-receiving device 30 that receives reflected light from the object to be measured 10 based on the pulsed light applied by the light source unit 20, and a host 40.

[0311] In the light-receiving device 30 that is a ToF sensor using a ToF method, the pixel value D output from the addition unit 33 is directly input to the histogram addition processing unit 34 and the ambient light estimation processing unit 62 in a logarithmic representation, and the ambient light estimation processing unit 62 calculates an arithmetic mean and a variance of an ambient light estimation process in a logarithmic representation.

[0312] The ambient light estimation processing unit 62 in a logarithmic representation can sample the pixel value D at a plurality of times t in a predetermined measurement period, and output an image in which a logarithmic representation data LogSUM obtained by transforming the sum SUM of the sampled pixel values D t into a logarithmic value or an approximate value thereof is used as a pixel value. In other words, the light-receiving device 30 according to Example 3 is a ToF sensor capable of not only outputting distance measurement information but also outputting an image constituted by pixel values subjected to logarithmic transformation.

[0313] [Example of a method for calculating an arithmetic mean value and a variance of ambient light in a logarithmic expression]

[0314] First, with respect to the arithmetic mean value μ of the ambient light, the following is calculated:

[0315] [mathematical formula 1]

[0316] As

[0317]

[0318] The approximation value S of the logarithm of the sum SUM is sequentially approximated, and the inverse transformation (2 x -1) from log2(1+μ)=S-log2N is performed to obtain the arithmetic mean value μ of the ambient light. Here, N is the number of samples, and log2N is the logarithmic value of the number of samples N or an approximation thereof.

[0319] It is assumed that the intensity estimation of the ambient light is calculated as AMP·μ+OFFSET based on the arithmetic mean value μ of the ambient light using a predetermined multiplier AMP and a predetermined addend OFFSET, and the intensity estimation of the ambient light can be adjusted by the multiplier AMP and the addend OFFSET.

[0320] With respect to the variance σ 2 , first,

[0321] [mathematical formula 2]

[0322] As

[0323]

[0324] SS is sequentially approximated.

[0325] Next, as

[0326] [mathematical formula 3]

[0327]

[0328] [mathematical formula 4]

[0329]

[0330] 2(S-log2N) and SS-log2N (=MM) are obtained by addition / subtraction and shifting on the logarithmic expression.

[0331] With respect to the variance σ 2 ,

[0332] Because [mathematical formula 5]

[0333]

[0334] is established, so the variance σ 2 The approximation value V is obtained by taking 2(S-log2N) and by inverting the value SS-log2N to 2 x obtained by the difference.

[0335] Since the standard deviation σ is the square root of the variance σ 2 , the value obtained by performing a logarithmic transformation, dividing the result by 2, and performing an inverse transformation on the result (as Equations (6) and (7) below) is used as the approximation value.

[0336] [mathematical formula 6]

[0337]

[0338] [mathematical formula 7]

[0339]

[0340] [First circuit example for calculating the arithmetic mean and variance of the ambient light in a logarithmic representation]

[0341] Figure 35 is a block diagram of a first circuit example showing a circuit portion in the ambient light estimation processing unit 62 according to Example 3 that calculates the arithmetic mean and variance of the ambient light in a logarithmic representation.

[0342] The ambient light estimation processing unit 62 includes a D flip-flop 6251, a logarithmic transformation unit 6252, a D flip-flop 6253, an approximation value calculation unit 6254, a D flip-flop 6255, a subtracter 6256, a log2N setting unit 6257, a D flip-flop 6258, an adder 6259, a log2AMP setting unit 6260, a logarithmic inverse transformation unit 6261, an adder 6262, an OFFSET-AMP+1 setting unit 6263, and a D flip-flop 6264 as circuitry for calculating the ambient light intensity estimate.

[0343] During the time period in which the arithmetic mean and variance of the ambient light are acquired, the D flip-flop 6251, the D flip-flop 6253, and the D flip-flop 6255 are enabled. Each of the D flip-flop 6258 and the D flip-flop 6264 is enabled for one cycle, thereby causing the pipeline to flow once at the end of the time period in which the arithmetic mean and variance of the ambient light are acquired.

[0344] The D flip-flop 6251 receives as input the pixel value D t obtained by sampling the pixel value D at a plurality of times t in a predetermined measurement period. When enabled, the D flip-flop 6251 latches the pixel value D t The logarithmic transformation unit 6252 performs a logarithmic transformation on the pixel value D tA logarithmic transformation of log2(1 + x) is performed. When enabled, the D flip-flop 6253 accumulatively adds the transformed result log2(1 + D of the logarithmic transformation unit 6252 t ) of the logarithmic transformation unit 6252.

[0345] The approximation value calculation unit 6254 performs approximation value calculation based on the output of the D flip-flop 6253 and the output of the D flip-flop 6255. The D flip-flop 6255 outputs S of the formula (1) (i.e., an approximation value of the logarithmic representation data LogSUM) as a pixel value of a display image. The output S of the D flip-flop 6255 is also input to the subtracter 6256. The subtracter 6256 subtracts log2N from the output S of the D flip-flop 6255.

[0346] When enabled, the D flip-flop 6258 latches the subtraction result of the subtracter 6256. The adder 6259 adds log2AMP to the output of the D flip-flop 6258. The logarithmic inverse transformation unit 6261 performs a 2 x -1 inverse logarithmic transformation on the addition result of the adder 6259. The adder 6262 adds OFFSET-AMP+1 to the inverse transformed result of the logarithmic inverse transformation unit 6261. When enabled, the D flip-flop 6264 latches the addition result of the adder 6262 and outputs the result as an ambient light intensity estimate.

[0347] The ambient light estimate processing unit 62 includes a 1-bit left shift circuit 6265, an approximation value calculation unit 6266, a D-flip-flop 6267, a subtracter 6268, a D-flip-flop 6269, a logarithmic inverse transformation unit 6270, a subtracter 6273, a 1-bit left shift circuit 6272, a logarithmic inverse transformation unit 6270, a D-flip-flop 6274, a logarithmic transformation unit 6275, a 1-bit right shift circuit 6276, a logarithmic inverse transformation unit 6277, and a D-flip-flop 6278 as circuitry for calculating an approximation value of a standard deviation.

[0348] The D flip-flop 6267 is enabled for a period in which an arithmetic mean value and a variance of ambient light are acquired. Each of the D-flip-flop 6269 and the D-flip-flop 6274 is enabled for one cycle, so that the pipeline flows once at the end of the period in which the arithmetic mean value and the variance of ambient light are acquired.

[0349] The output of the D flip-flop 6253 is supplied to the approximation value calculation unit 6266 via the 1-bit left shift circuit 6265. The approximation value calculation unit 6266 performs approximation value calculation based on the output of the D flip-flop 6253 which is shifted one bit to the left by the 1-bit left shift circuit 6265 and the output of the D flip-flop 6267. The D flip-flop 6267 outputs SS of the formula (2).

[0350] Subtracter 6268 subtracts log2N from the output SS of D flip-flop 6267. When enabled, D flip-flop 6269 latches the subtraction result of subtracter 6268. Logarithmic inverse transform unit 6270 performs 2 x inverse transform on the output of D flip-flop 6269. Logarithmic inverse transform unit 6271 performs 2 x inverse transform on the output of D flip-flop 6258 which is shifted one bit to the left by 1-bit left shift circuit 6272.

[0351] Subtracter 6273 performs subtraction between the inverse transform result of logarithmic inverse transform unit 6270 and the inverse transform result of logarithmic inverse transform unit 6271. When enabled, D flip-flop 6274 latches the subtraction result of subtracter 6273 and outputs the result as the variance σ 2 of ambient light. 2 Logarithmic transform unit 6275 performs log2(x) logarithmic transform on the output of D flip-flop 6274, i.e., the variance σ

[0352] 1-bit right shift circuit 6276 shifts the transform result of logarithmic transform unit 6275 only one bit to the right. Logarithmic inverse transform unit 6277 performs 2 x inverse transform on the output of 1-bit right shift circuit 6276. D flip-flop 6278 latches the inverse transform result of logarithmic inverse transform unit 6277 and outputs the result as an approximation of the standard deviation.

[0353] [Second circuit example for calculating the arithmetic mean and variance of the ambient light in logarithmic representation]

[0354] Figure 36 is a block diagram showing a second circuit example of a circuit portion for calculating the arithmetic mean and variance of the ambient light in logarithmic representation in the ambient light estimation processing unit 62 according to Example 3.

[0355] In the first circuit example, an approximation of the logarithmic representation data LogSUM output as the output S of D flip-flop 6255 is output as a pixel value of a display image. On the other hand, in the second circuit example, the logarithmic representation data LogSUM is calculated from the pixel value D t which is latched by D flip-flop 6201 and output as a pixel value of a display image.

[0356] Specifically, as Figure 36 shown, the ambient light estimation processing unit 62 includes subtracter 6279, D flip-flop 6280, and logarithmic transform unit 6281 as a circuit system for calculating the logarithmic representation data LogSUM.

[0357] During acquisition of the arithmetic average value and the variance of the ambient light, the D flip-flop 6280 is enabled. The adder 6279 and the D flip-flop 6280 perform cumulative addition of the pixel values D t The log conversion unit 6281 performs log2(l+x) log conversion on the cumulative addition result of the pixel values D t and outputs the log representation data LogSUM as a result of the conversion as the pixel value of the display image.

[0358] Meanwhile, in the first circuit instance and the second circuit instance, the approximate value calculation LogAdd(a, b) of the approximate value calculation unit 6266 and the approximate value calculation unit 6254 is calculated using the approximate expression of the following formula (8).

[0359] [Mathematical Formula 8]

[0360]

[0361] As in the following formula (9), the calculation of the contents of the logarithm added in the logarithm is performed with a fixed-point number.

[0362] [Mathematical Formula 9]

[0363]

[0364] Here, let

[0365] [Mathematical Formula 10]

[0366]

[0367] Let f(x) be a fixed-point number having w bits after the decimal point, 2 -ldl can be approximated by the following formula (11).

[0368] [Mathematical Formula 11]

[0369]

[0370] LogAdd(a, b) is a fixed-point number having w bits after the decimal point, and is expressed as follows:

[0371] [Mathematical Formula 12]

[0372]

[0373] and can be implemented by a comparator, a shift circuit, and an adder.

[0374] <<Embodiment 4>>

[0375] Embodiment 4 is a log conversion unit 65 in the light receiving device 30 according to Embodiment 1 or Embodiment 2 (seeFigure 13 or 31).

[0376] [First Specific Example]

[0377] The first specific example is an example in which the cumulative histogram of the pixel values in the logarithmic representation is further subjected to a logarithmic transformation and compression. This is an example in which the cumulative values of the histogram are subjected to a logarithmic transformation and compression. Figure 37A is a block diagram showing a first specific example of the logarithmic transformation unit 65 according to Embodiment 4.

[0378] As shown in Figure 37A , the logarithmic transformation unit 65 according to the first specific example includes a logarithmic transformer 651, a clip circuit 652, and a D flip-flop 653, and is configured to perform a logarithmic transformation on the cumulative values of the histogram of the pixel values in the logarithmic representation to compress the result.

[0379] The logarithmic transformation unit 65 receives an input of the histogram data smoothed by the smoothing filter 64 in the logarithmic representation shown in Figure 13 or Figure 31 , for example, data of about 10 bits to 16 bits.

[0380] The logarithmic transformer 651 performs a logarithmic transformation of log2(1+x) on the smoothed histogram data. The clip circuit 652 saturates the value to 7 or more to 7 for the transformation result of the logarithmic transformer 651. The D flip-flop 653 latches the output of the clip circuit 652 to output the result as 3-bit data having a value of 0 to 7.

[0381] [Second Specific Example]

[0382] The second specific example is an example in which the cumulative histogram of the pixel values in the logarithmic representation is further subjected to a logarithmic transformation and compressed after subtracting the minimum value. Figure 37B is a block diagram showing a second specific example of the logarithmic transformation unit 65 according to Embodiment 4.

[0383] As shown in Figure 37B , the logarithmic transformation unit 65 according to the second specific example includes, in addition to the logarithmic transformer 651, the clip circuit 652, and the D flip-flop 653, a subtracter 654 of a preceding stage of the logarithmic transformer 651, and is configured to further perform a logarithmic transformation on the cumulative histogram in the logarithmic representation to compress the result after the subtraction with the minimum value of the cumulative histogram.

[0384] The logarithmic transformation unit 65 receives an input of the histogram data smoothed by the smoothing filter 64 in the logarithmic representation shown in Figure 13 or Figure 31 , for example, data of about 10 bits to 16 bits.

[0385] The subtracter 654 subtracts the minimum value of the smoothed histogram data from the smoothed histogram data. The logarithmic converter 651 performs a logarithmic conversion of log2(l+x) on the subtraction result of the subtracter 654. The clipping circuit 652 saturates 7 or more to 7 for the conversion result of the logarithmic converter 651. The D flip-flop 653 latches the output of the clipping circuit 652 to output the result as 3-bit data having a value of 0 to 7.

[0386] According to the logarithmic conversion unit 65 according to the second specific example having the above-described configuration, in the case of compressing from 10 bits to 3 bits, the compression can be reduced to 30%. Further, in the case of compressing from 16 bits to 3 bits, the compression can be reduced to 19%.

[0387] Regarding the logarithm of the value obtained by subtracting the minimum value from the cumulative value of the histogram of the pixel value in the logarithmic representation, Figure 38A The logarithm in the case of once addition is shown, Figure 38B The logarithm in the case of four times addition is shown, Figure 39A The logarithm in the case of 16 times addition is shown, and Figure 39B The logarithm in the case of 32 times addition is shown.

[0388] Further, regarding the logarithm of the value obtained by subtracting the minimum value from the cumulative value of the histogram of the pixel value in the logarithmic representation obtained by subtracting the arithmetic mean value of the ambient light, Figure 40A The logarithm in the case of once addition is shown, Figure 40B The logarithm in the case of four times addition is shown, Figure 41A The logarithm in the case of 16 times addition is shown, and Figure 41B The logarithm in the case of 32 times addition is shown.

[0389] <<Embodiment 5>>

[0390] Embodiment 5 is an example of reduction of memory capacity by data compression of the cumulative histogram of the pixel value in the logarithmic representation, and is another configuration example of the histogram addition processing unit 63 of the logarithmic representation in the light receiving device according to Embodiment 1.

[0391] [Configuration example of system]

[0392] Figure 42 is a block diagram showing a configuration example of the histogram addition processing unit 63 of the logarithmic representation according to Embodiment 5. The histogram addition processing unit 63 according to Embodiment 5 has a configuration in which a data compression / decompression function in which difference encoding performed in the form of a difference of sequential data is installed before and after the SRAM 633, which is an example of a memory that stores data of the logarithmic representation.

[0393] Specifically, as shown in Figure 42 The encoding circuit 641 is installed on the input stage of the SRAM 633 on the side of the input write address WRITE_ADDR (WA) and the write data WRITE_DATA (WD), and the decoding circuit 642 is installed on the output stage of the SRAM 633 on the side of the input read address READ_ADDR (RA). Figure 43 A flow of the differential encoding of the cumulative histogram of the logarithmic representation is shown.

[0394] As described above, by installing the data compression / decompression function by the differential encoding before and after the SRAM 633, the memory capacity of the SRAM 633 can be reduced. As an example, Figure 44A The data size in the case where the histogram of 048 groups is stored in the SRAM 633 without being compressed is shown, and Figure 44B The data size in the case where the differential encoding is performed is shown.

[0395] For example, assuming that the number of escapes is 256 or less, the capacity of the escape memory 6332 (see Figure 45 ) of the SRAM 633 is reduced. In the case of 256 escapes, compression to 50.0% [(3 x 2048 + 8 x 256) / (8 x 2048)] can be performed, and in the case of 64 escapes, compression to 40.6% [(3 x 2048 + 8 x 64) / (8 x 2048)] can be performed.

[0396] [Configuration example of encoding circuit]

[0397] Figure 45 is a block diagram showing a configuration example of the encoding circuit 641. Meanwhile, the SRAM 633 includes the code memory 6331 and the escape memory 6332. The write address WA inputted from the D flip-flop 637 in the histogram addition processing unit 63 t is written in the code memory 6331.

[0398] As shown in Figure 45 , the encoding circuit 641 includes the D flip-flop 6411, the subtracter 6412, the code assignment processing unit 6413, the adder (+1) 6414, and the D flip-flop 6415.

[0399] The D flip-flop 6411 latches the write data WD inputted from the D flip-flop 632 t in the histogram addition processing unit 63. The subtracter 6412 subtracts the latched data WD t of the D flip-flop 6411 from the write data WD t-1 inputted from the D flip-flop 632.

[0400] The code allocation processing unit 6413 adds the write data WD t and the subtraction result of the subtractor 6412 (WD t -WD t-1 ), and provides the write data SingWD t , Abs t to the code memory 6331 and the write data EscapeWD t to the escape memory 6332.

[0401] The adder 6414 and the D flip-flop 6415 count up (increment) the write address EscapeWA of the escape memory 6332 every time an escape code can be generated.

[0402] [Configuration example of decoding circuit]

[0403] Figure 46 is a block diagram showing a configuration example of the decoding circuit 642. As Figure 46 shown in the drawing, the decoding circuit 642 includes a multiplier 6421, an adder 6422, a D flip-flop 6423, a selector 6424, an escape determination unit 6425, an adder (+1) 6426, and a D flip-flop 6427.

[0404] The multiplier 6421 multiplies the read data SingWD t input from the code memory 6331 by the read data Abs t . The adder 6422 adds the latch data RD t-1 of the D flip-flop 6423 to the multiplication result (SingWD t x Abs t ) of the multiplier 6421. The D flip-flop 6423 latches the read data RD t output from the selector 6424.

[0405] The selector 6424 receives two inputs of the addition result of the adder 6422 and the read data EscapeRD t read out from the escape memory 6332, selects either of the two inputs based on the determination result of the escape determination unit 6425, and outputs the selected one as the read data RD t . The escape determination unit 6425 performs escape determination based on the read data Abs t input from the code memory 6331.

[0406] The adder 6426 and the D flip-flop 6427 count up (increment) the write address EscapeWA of the escape memory 6332 every time an escape code is read out.

[0407] <Effects of the first embodiment>

[0408] According to the first embodiment, the following functional effects can be obtained.

[0409] (Improvement of dynamic range or reduction of memory capacity)

[0410] While there is a trade-off between the dynamic range of the histogram and the memory size, for the same memory size, the dynamic range is larger than that in the conventional method. Therefore, even if the number of laser emissions is increased in order to improve the S / N, the histogram is not saturated, making it possible to prevent degradation of the accuracy of the position determination of the reflected light.

[0411] In the case of the same dynamic range, since the memory size can be reduced, the circuit size can be reduced.

[0412] (Reduction of power consumption)

[0413] By reducing the bit depth in the logarithmic representation (for example, reduction from 12 bits in the linear representation to 8 bits in the logarithmic representation), the bit depth of the D flip-flop (FF) and the memory is reduced, making it possible to reduce the power consumption at the time of the histogram processing.

[0414] For the variance calculation, a square root arithmetic unit is not required, and instead, an adder / subtractor and a simple circuit for logarithmic conversion and inverse conversion can be used, resulting in reduction of power consumption.

[0415] [Functional effects of the ambient light estimation processing based on the geometric mean value]

[0416] It is less likely to be affected by temporary large fluctuations in the ambient light.

[0417] Even for a sample including reflected light, it is possible to calculate a value close to the average value of the ambient light.

[0418] (Functional effects of lossy compression of the histogram obtained by further logarithmic conversion of the logarithmic accumulation)

[0419] The compressed data makes it possible to reduce the necessary data transmission band, shorten the transmission time, and reduce the number of pins of the LSI.

[0420] (Functional effects of differential encoding of the logarithmic representation)

[0421] Since the bit depth is reduced by the logarithmic representation, the bit depth of the escape code can be reduced, and the storage capacity of the escape SRAM can be reduced. Furthermore, since a 2-bit code SRAM and an escape SRAM are sufficient, it is possible to reduce the storage capacity of the SRAM, and it is possible to reduce the circuit size and the power consumption by reducing the bit depth of the ECC circuit. ​

[0422] (logarithmic cumulative effect)

[0423] When 2 k -1≤a≤2 k+1 -1, k=0, 1,... remains,

[0424] [mathematical formula 13]

[0425]

[0426] can be approximated by a broken line.

[0427] Let

[0428] [mathematical formula 14]

[0429]

[0430] where s (≥ 0) is the number of SPAD elements that have reacted to reflected light, and L independent random variables X i The expected value μ sl of the sum of the logarithms log2(1+X i ) is given by

[0431] [mathematical formula 15]

[0432]

[0433] and the variance σ sl 2 is given by

[0434] [mathematical formula 16]

[0435]

[0436] Here, assume l=k,

[0437] [mathematical formula 17]

[0438]

[0439] remains.

[0440] When 2 k -1≤μ e / (1+s)≤2 k+1 -1, 2 k -1≤e i / (1+s)≤2 k+1 -1, and k=0, 1,... remains, the expected value μ s1 can be approximated as Llog2(1+s+μ e ), and the standard deviation σ s1It can be approximated as {√L / (1+s)2 k}σ e .

[0441] As mentioned above, the expected value μ sl Proportional to L; however, the standard deviation σ sl is proportional to √L, which is similar to those in the linear representation. In addition, the standard deviation σ sl It is inversely proportional to the amplitude s of the signal level, and when the amplitude s of the signal level is small, the standard deviation σ sl With noise range 2 k Inversely proportional.

[0442] Figure 47 The cumulative histogram of the logarithmic representation is shown when 16 additions are performed without deducting the geometric mean of the ambient light. The larger the signal level, the smaller the standard deviation of the logarithmic accumulation.

[0443] Figure 48 The cumulative histogram of logarithmic representation is shown for 16 additions with subtraction of the geometric mean of ambient light. When the geometric mean of ambient light is subtracted, the standard deviation of the logarithmic accumulation is not reduced because the signal level in the area without reflected light is small; however, the signal level of reflected light is not that small.

[0444] (The effect of noise reduction is reduced by averaging in synchronous addition)

[0445] The geometric mean becomes smaller than the arithmetic mean, and when there are large outliers, the arithmetic mean does not match the location of the distribution peak, but the geometric mean tends to match.

[0446] When 2 k -1≤μ e / (1+s)≤2 k+1 -1 hour, 2 k -1≤e i / (1+s)≤2 k+1 -1, k=0, 1, ..., keep, expected value μ s1 It can be approximated as Llog2(1+s+μ e ). L multiplied by log2(1+x i ) is the arithmetic mean

[0447] [Mathematical formula 18]

[0448]

[0449] And it is 1+x i The expected value μ of the logarithm of the geometric mean geoTherefore, by multiplying the expected value μ geo of the logarithm of the geometric mean by L, the cumulative of L multiplied by log2(1+x i ) is obtained.

[0450] In a case where the distribution includes large values, the arithmetic mean tends to be larger than the median. In this case, the geometric mean has a less large characteristic. Since the cumulative of log2(1+x i ) is also performed L times, this characteristic is also present, and therefore, for example, in a case where the distance measurement device of the present disclosure is installed on a vehicle control system and used, even if large values are mixed several times by accident in the laser emission performed L times due to the headlight or the like of an oncoming vehicle, this cumulative is hardly affected.

[0451] Figure 49A The difference between the geometric mean and the arithmetic mean is shown for the case of noise averaging by synchronous addition, and Figure 49B A histogram of the data values (output values of the SPAD elements) is shown.

[0452] (Effect of averaging in the time direction)

[0453] As in the case of noise averaging by synchronous addition, the geometric mean becomes smaller than the arithmetic mean, and when there is a large abnormal value, the arithmetic mean does not match the position of the peak of the distribution, but the geometric mean tends to match.

[0454] In the estimation of the ambient light intensity estimation, when the geometric mean is taken in a state where the reflected light is mixed, this value becomes close to the arithmetic mean of the arithmetic mean of the ambient light, without being greatly affected by the reflected light. Figure 50A The difference between the geometric mean and the arithmetic mean is shown in a case where averaging is performed in the time direction, and Figure 50B A histogram of the data values (pixel values) is shown.

[0455] <Second Embodiment of the Present Disclosure>

[0456] In the first embodiment, a distance measurement device called a flash type was described as an example. In contrast, in the second embodiment, a distance measurement device called a scanning type is described as an example. In addition, in the following description, the same reference numerals are given to the same structures as those of the first embodiment, and repeated description is omitted.

[0457] [Example of System Configuration of Distance Measurement Device]

[0458] Figure 51 is a schematic view showing an example of the schematic configuration of a distance measurement device according to the second embodiment of the present disclosure. As Figure 51As shown, the distance measuring device according to the second embodiment includes, in addition to the light source unit 20 and the light receiving device 30, a control device 200, a condensing lens 201, a half mirror 202, a micro mirror 203, a light receiving lens 204, and a scanner unit 205.

[0459] The micro mirror 203 and the scanner unit 205 constitute a scanning unit that scans light incident on the light receiving unit 32 of the light receiving device 30. Note that, in addition to the micro mirror 203 and the scanner unit 205, the scanning unit can include at least one of the condensing lens 201, the half mirror 202, and the light receiving lens 204.

[0460] As in the case of the first embodiment, the light source unit 20 includes, for example, one or more semiconductor laser diodes, and emits pulsed laser light Ll having a predetermined time width at a predetermined emission period. Further, the light source unit 20 emits laser light Ll having a time width of 1 nanosecond at a period of, for example, 1 gigahertz (GHz).

[0461] The condensing lens 201 condenses the laser light Ll emitted from the light source unit 20. For example, the condensing lens 201 condenses the laser light Ll so that the spread of the laser light Ll is about the same as the angle of view of the light receiving surface of the light receiving device 30.

[0462] The half mirror 202 reflects at least a portion of the incident laser light Ll toward the micro mirror 203. Note that, instead of the half mirror 202, an optical element that reflects a portion of light and transmits another portion of light, such as a polarizing mirror, can also be used.

[0463] The micro mirror 203 is attached to the scanner unit 205 so that the angle can be changed with the center of the reflecting surface as an axis. For example, the scanner unit 205 swings or vibrates the micro mirror 203 in the horizontal direction so that the image SA of the laser light Ll reflected by the micro mirror 203 reciprocates horizontally in the predetermined scanning region AR. For example, the scanner unit 205 swings or vibrates the micro mirror 203 in the horizontal direction so that the image SA of the laser light Ll reciprocates in the predetermined scanning region AR within 1 millisecond. Note that a stepping motor, a piezoelectric element, or the like can be used to swing or vibrate the micro mirror 203.

[0464] The reflected light L2 of the laser light Ll reflected by the object 90 present in the distance measurement range is incident on the micro mirror 203 from a direction opposite to the laser light Ll, with the same optical axis as the emission axis of the laser light Ll as the incident axis. The reflected light L2 incident on the micro mirror 203 enters the half mirror 202 along the same optical axis as the laser light Ll, and a portion thereof passes through the half mirror 202.

[0465] An image of the reflected light L2 through the half-mirror 202 is formed on a pixel column in the light-receiving unit 32 of the light-receiving device 30 by the light-receiving lens 204.

[0466] The light-receiving device 30 can have a configuration similar to that of the light-receiving device (specifically, the light-receiving device according to each example of the first embodiment) exemplified in the first embodiment. Other configurations and operations can be similar to those of the first embodiment. Therefore, detailed description is omitted here.

[0467] In the light-receiving device 30, the light-receiving unit 32 has a structure in which, for example, the pixels 60 exemplified in the first embodiment are arranged in the vertical direction (corresponding to the row direction). That is, the light-receiving unit 32 can be configured by, for example, some rows (one row or several rows) of the SPAD array unit 323 shown in FIG. 8. Figure 15

[0468] The control device 200 is realized by, for example, an information processing device such as a central processing unit (CPU), and controls the light source unit 20, the light-receiving device 30, the scanner unit 205, and the like.

[0469] <<Functional Effects of the Second Embodiment>>

[0470] As described above, the technology according to the present disclosure is applicable not only to a flash-type distance measuring device but also to a scanning-type distance measuring device. Also, in the scanning-type distance measuring device, by using the light-receiving device of each example of the first embodiment as the light-receiving device 30, the same functional effects as in the case of the first embodiment can be obtained.

[0471] Although the embodiments of the present disclosure have been described above, the technical scope of the present disclosure is not limited to the above-described embodiments themselves and various modifications can be made without departing from the spirit of the present disclosure. Further, constituent elements of different embodiments and modified examples can be combined as appropriate.

[0472] Furthermore, the effects described in the embodiments described in the present specification are merely examples and are not limiting, and there can be other effects.

[0473] <Examples of Application of the Technology According to the Present Disclosure>

[0474] The technology according to the present disclosure can be applied to various products. In the following, more specific examples of application are described. For example, the technology according to the present disclosure can be realized as a distance measuring device mounted on any type of mobile object, such as a car, an electric vehicle, a hybrid electric vehicle, a motorcycle, a bicycle, personal mobility, an airplane, a drone, a ship, a robot, a construction machine, an agricultural machine (tractor), and the like.

[0475] ​[mobile body]

[0476] Figure 52 is a block diagram of an example of a schematic configuration of a vehicle control system 7000 that is an example of depicting a mobile body control system to which the technology according to the embodiments of the present disclosure is applicable. The vehicle control system 7000 includes a plurality of electronic control units connected to each other via a communication network 7010. In the example shown, the vehicle control system 7000 includes a drive system control unit 7100, a body system control unit 7200, a battery control unit 7300, an outside-vehicle information detection unit 7400, an on-vehicle information detection unit 7500, and an integrated control unit 7600. The communication network 7010 that connects the plurality of control units to each other can be, for example, an in-vehicle communication network in compliance with an arbitrary standard, such as a controller area network (CAN), a local interconnect network (LIN), a local area network (LAN), FlexRay (registered trademark), or the like. Figure 52

[0477] Each control unit includes a microcomputer that performs arithmetic operation processing according to various programs, a storage section that stores programs executed by the microcomputer, parameters for various operations, and the like, and a drive circuit that drives various control target devices. Each control unit further includes a network interface (I / F) for performing communication with other control units via the communication network 7010, and a communication I / F for communicating with devices, sensors, and the like inside and outside the vehicle by wired or wireless communication. Figure 52 The functional configuration of the integrated control unit 7600 shown includes a microcomputer 7610, a general-purpose communication I / F 7620, a dedicated communication I / F 7630, a positioning section 7640, a beacon reception section 7650, a vehicle-mounted device I / F 7660, a sound / image output section 7670, a vehicle-mounted network I / F 7680, and a storage section 7690. The other control units similarly include a microcomputer, a communication I / F, a storage section, and the like.

[0478] The drive system control unit 7100 controls the operation of devices related to the drive system of the vehicle according to various programs. For example, the drive system control unit 7100 functions as a control device for a drive force generation device such as an internal combustion engine, a drive motor, or the like that generates a drive force of the vehicle, a drive force transmission mechanism that transmits the drive force to wheels, a steering mechanism that adjusts a steering angle of the vehicle, a brake device that generates a braking force of the vehicle, and the like. The drive system control unit 7100 can have a function as a control device of an anti-lock brake system (ABS), an electronic stability control (ESC), or the like.

[0479] ​The drive system control unit 7100 is connected with a vehicle state detection portion 7110. The vehicle state detection portion 7110 includes, for example, at least one of a gyro sensor that detects an angular velocity of an axial rotational motion of a vehicle body, an acceleration sensor that detects an acceleration of the vehicle, and a sensor that detects an operation amount of an accelerator pedal, an operation amount of a brake pedal, a steering angle of a steering wheel, an engine rotation speed, or a wheel rotation speed. The drive system control unit 7100 performs an arithmetic processing using a signal input from the vehicle state detection portion 7110, and controls an internal combustion engine, a drive motor, an electric power steering device, a brake device, and the like.

[0480] The body system control unit 7200 controls operations of various devices provided to a vehicle body in accordance with various programs. For example, the body system control unit 7200 functions as a control device for a keyless entry system, a smart key system, a power window device, or various lamps such as a headlamp, a backup lamp, a brake lamp, a turn signal, a fog lamp, and the like. In this case, radio waves emitted from a mobile device can be input to the body system control unit 7200 as a substitute for signals of a key or various switches. The body system control unit 7200 receives these input radio waves or signals, and controls a door lock device, a power window device, a lamp, and the like of the vehicle.

[0481] The battery control unit 7300 controls a secondary battery 7310 that is a power supply for driving a motor in accordance with various programs. For example, information about a battery temperature, a battery output voltage, a remaining charge amount in the battery, and the like is supplied from a battery device including the secondary battery 7310 to the battery control unit 7300. The battery control unit 7300 performs an arithmetic processing using these signals, and performs a control for adjusting a temperature of the secondary battery 7310 or a control of a cooling device provided to the battery device and the like.

[0482] The outside-vehicle information detection unit 7400 detects information outside a vehicle including the vehicle control system 7000. For example, the outside-vehicle information detection unit 7400 is connected with at least one of an imaging portion 7410 and an outside-vehicle information detection portion 7420. The imaging portion 7410 includes at least one of a time-of-flight (ToF) camera, a stereo camera, a monocular camera, an infrared camera, and other cameras. For example, the outside-vehicle information detection portion 7420 includes at least one of an environmental sensor for detecting a current atmospheric condition or a weather condition, and a peripheral information detection sensor for detecting other vehicles, obstacles, pedestrians, and the like in a periphery of a vehicle including the vehicle control system 7000.

[0483] For example, the environmental sensor can be at least one of a raindrop sensor that detects rain, a mist sensor that detects mist, a sunlight sensor that detects the degree of sunlight, and a snow sensor that detects snowfall. The peripheral information detection sensor can be at least one of an ultrasonic sensor, a radar device, and a LIDAR (Light Detection and Ranging, or Laser Imaging Detection and Ranging) device. Each of the imaging section 7410 and the outside-vehicle information detection section 7420 can be provided as an independent sensor or device, or can be provided as a device in which a plurality of sensors or devices are integrated.

[0484] Here, Figure 53 Examples of mounting positions of the imaging sections 7410 and the outside-vehicle information detection sections 7420 are shown. The imaging sections 7910, 7912, 7914, 7916, and 7918 are provided, for example, at least one of positions on the front nose, side mirrors, rear bumper, and rear door of the vehicle 7900 and a position on the upper portion of the windshield in the vehicle interior. The imaging section 7910 provided on the front nose portion in the vehicle interior and the imaging section 7918 provided on the upper portion of the windshield mainly obtain images of the front of the vehicle 7900. The imaging sections 7912 and 7914 provided on the side mirrors mainly obtain images of the side of the vehicle 7900. The imaging section 7916 provided on the rear bumper or the rear door mainly obtains images of the rear of the vehicle 7900. The imaging section 7918 provided on the upper portion of the windshield in the vehicle interior is mainly used for detecting a preceding vehicle, a pedestrian, an obstacle, a signal, a traffic sign, a lane, and the like.

[0485] Incidentally, Figure 53 Examples of imaging ranges of the respective imaging sections 7910, 7912, 7914, and 7916 are shown. The imaging range a indicates the imaging range of the imaging section 7910 provided to the front nose. The imaging ranges b and c indicate the imaging ranges of the imaging sections 7912 and 7914 provided to the side mirrors, respectively. The imaging range d indicates the imaging range of the imaging section 7916 provided to the rear bumper or the rear door. For example, by superimposing image data imaged by the imaging sections 7910, 7912, 7914, and 7916, a bird's-eye image of the vehicle 7900 viewed from above can be obtained.

[0486] The outside-vehicle information detection sections 7920, 7922, 7924, 7926, 7928, 7930 provided on the front, rear, side, corners, and the upper portion of the windshield in the vehicle interior of the vehicle 7900 can also be, for example, ultrasonic sensors or radar devices. The outside-vehicle information detection sections 7920, 7926, 7930 provided on the front nose of the vehicle 7900, the rear bumper, the rear door of the vehicle 7900, the upper portion of the windshield in the vehicle interior can also be, for example, LIDAR devices. These outside-vehicle information detection sections 7920 to 7930 are mainly used for detecting a preceding vehicle, a pedestrian, an obstacle, and the like.

[0487] Return Figure 52 will be continued. The outside-vehicle information detecting unit 7400 causes the imaging section 7410 to take an image of the outside of the vehicle, and receives the taken image data. In addition, the outside-vehicle information detecting unit 7400 receives detection information from the outside-vehicle information detecting section 7420 connected to the outside-vehicle information detecting unit 7400. In a case where the outside-vehicle information detecting section 7420 is an ultrasonic sensor, a radar device, or a LIDAR device, the outside-vehicle information detecting unit 7400 transmits an ultrasonic wave, an electromagnetic wave, or the like, and receives information of a reflected wave received. The outside-vehicle information detecting unit 7400 can perform processing of detecting an object such as a human, a vehicle, an obstacle, a sign, a character on a road surface, or the like, or processing of detecting a distance to the object, on the basis of the received information. In addition, the outside-vehicle information detecting unit 7400 can perform environmental recognition processing of recognizing rain, fog, a road surface condition, or the like, on the basis of the received information. The outside-vehicle information detecting unit 7400 can calculate a distance to an object outside the vehicle on the basis of the received information.

[0488] In addition, the outside-vehicle information detecting unit 7400 can perform image recognition processing of recognizing a human, a vehicle, an obstacle, a sign, a character on a road surface, or the like, or processing of detecting a distance thereto, on the basis of the received image data. The outside-vehicle information detecting unit 7400 can perform processing such as distortion correction, alignment, or the like, on the received image data, and combine image data imaged by a plurality of different imaging sections 7410 to generate an aerial view image or a panoramic image. The outside-vehicle information detecting unit 7400 can perform viewpoint conversion processing using image data taken by the imaging section 7410 including photographing sections different from each other.

[0489] The in-vehicle information detecting unit 7500 detects information about the inside of the vehicle. For example, the in-vehicle information detecting unit 7500 is connected to a driver state detecting section 7510 that detects a state of a driver. The driver state detecting section 7510 can include a camera that images the driver, a biological sensor that detects biological information of the driver, a microphone that collects sound within the inside of the vehicle, or the like. The biological sensor is provided in, for example, a seat surface, a steering wheel, or the like, and detects biological information of a passenger seated on the seat or the driver holding the steering wheel. On the basis of detection information input from the driver state detecting section 7510, the in-vehicle information detecting unit 7500 can calculate a degree of fatigue of the driver or a degree of concentration of the driver, or can determine whether or not the driver dozes off. The in-vehicle information detecting unit 7500 can subject an audio signal obtained by collecting sound to processing such as noise canceling processing or the like.

[0490] The integrated control unit 7600 controls general operations within the vehicle control system 7000 in accordance with various programs. The integrated control unit 7600 is connected with an input portion 7800. The input portion 7800 is realized by a device capable of input operation by an occupant, such as a touch panel, a button, a microphone, a switch, a lever, or the like. The integrated control unit 7600 can be supplied with data obtained by voice recognition of a voice input through the microphone. The input portion 7800 can be, for example, a remote control device using infrared rays or another radio wave, or an external connection device, such as a mobile phone, a personal digital assistant (PDA), or the like, which supports operation of the vehicle control system 7000. The input portion 7800 can be, for example, a camera, and in this case, the occupant can input information by a gesture. Alternatively, data obtained by detecting movement of a wearable device worn by the occupant can be input. Further, the input portion 7800 can include, for example, an input control circuit or the like that generates an input signal based on information input by the occupant or the like using the above-described input portion 7800 and outputs the generated input signal to the integrated control unit 7600. The occupant or the like inputs various data or instructs processing operation to the vehicle control system 7000 by operating the input portion 7800.

[0491] The storage portion 7690 can include a read only memory (ROM) that stores various programs executed by the microcomputer and a random access memory (RAM) that stores various parameters, operation results, sensor values, and the like. Further, the storage portion 7690 can be realized by a magnetic storage device such as a hard disk drive (HDD), a semiconductor storage device, an optical storage device, a magneto-optical storage device, or the like.

[0492] The general-purpose communication I / F 7620 is a communication I / F that mediates communication with various devices existing in the external environment 7750, which is widely used. The general-purpose communication I / F 7620 can realize a cellular communication protocol such as Global System for Mobile Communications (GSM) (registered trademark), Worldwide Interoperability for Microwave Access (WiMAX), Long Term Evolution (LTE), Long Term Evolution-Advanced (LTE-A), or the like, or another wireless communication protocol such as Wireless LAN (also referred to as Wireless Fidelity (Wi-Fi (registered trademark)), Bluetooth (registered trademark), or the like. For example, the general-purpose communication I / F 7620 can be connected to a device (for example, an application server or a control server) existing on an external network (for example, the Internet, a cloud network, or a company-specific network) via a base station or an access point. Further, for example, the general-purpose communication I / F 7620 can be connected to a terminal existing in the vicinity of the vehicle, which is, for example, a terminal of a driver, a pedestrian, or a shop, or a machine type communication (MTC) terminal, using a peer-to-peer (P2P) technique.

[0493] The dedicated communication I / F 7630 is a communication I / F that supports development of a communication protocol for use in a vehicle. The dedicated communication I / F 7630 can implement a standard protocol, for example, such as Wireless Access in Vehicular Environments (WAVE), which is a combination of Institute of Electrical and Electronics Engineers (IEEE) 802.11p as a lower layer and IEEE 1609 as a higher layer, Dedicated Short-Range Communication (DSRC), or a cellular communication protocol. The dedicated communication I / F 7630 generally performs V2X communication as a concept including one or more of communication between vehicles (vehicle-to-vehicle), communication between a road and a vehicle (vehicle-to-infrastructure), communication between a vehicle and a home (vehicle-to-home), and communication between a pedestrian and a vehicle (vehicle-to-pedestrian).

[0494] The positioning section 7640 performs positioning, for example, by receiving a Global Navigation Satellite System (GNSS) signal (for example, a GPS signal from a Global Positioning System (GPS) satellite) from a GNSS satellite, and generates position information including the latitude, longitude, and altitude of the vehicle. Incidentally, the positioning section 7640 can identify the current position by exchanging signals with a wireless access point, or can obtain position information from a terminal such as a mobile phone, a Personal Handyphone System (PHS), or a smart phone having a positioning function.

[0495] The beacon receiving section 7650 receives, for example, radio waves or electromagnetic waves emitted from a radio station installed on a road or the like, and thereby obtains information on the current position, congestion, closed roads, necessary time, and the like. Incidentally, the function of the beacon receiving section 7650 can be included in the above-described dedicated communication I / F 7630.

[0496] The in-vehicle device I / F 7660 is a communication interface that mediates connection between the microcomputer 7610 and various in-vehicle devices 7760 present within the vehicle. The in-vehicle device I / F 7660 can establish a wireless connection using a wireless communication protocol such as wireless LAN, Bluetooth, Near Field Communication (NFC), or Wireless Universal Serial Bus (WUSB). Furthermore, the in-vehicle device I / F 7660 can establish a wired connection via a connection terminal (and a cable, if necessary) not shown in the drawing by Universal Serial Bus (USB), High-Definition Multimedia Interface (HDMI) (registered trademark), Mobile High-Definition Link (MHL), or the like. The in-vehicle devices 7760 can include, for example, at least one of a mobile device and a wearable device owned by an occupant, and an information device carried or attached to the vehicle. The in-vehicle devices 7760 can also include a navigation device that searches for a route to an arbitrary destination. The in-vehicle device I / F 7660 exchanges control signals or data signals with these in-vehicle devices 7760.

[0497] The in-vehicle network I / F 7680 is an interface that mediates communication of the microcomputer 7610 with the communication network 7010. The in-vehicle network I / F 7680 transmits and receives signals and the like in accordance with a predetermined protocol supported by the communication network 7010.

[0498] The microcomputer 7610 of the integrated control unit 7600 controls the vehicle control system 7000 in accordance with various programs on the basis of information obtained via at least one of the general-purpose communication I / F 7620, the dedicated communication I / F 7630, the positioning section 7640, the beacon receiving section 7650, the in-vehicle device I / F 7660, and the in-vehicle network I / F 7680. For example, the microcomputer 7610 can calculate a control target value of a driving force generation device, a steering mechanism, or a braking device on the basis of obtained information about the inside and outside of the vehicle, and output a control command to the drive system control unit 7100. For example, the microcomputer 7610 can perform cooperative control aimed at realizing a function of an advanced driver assistance system (ADAS) including collision avoidance or shock mitigation for the vehicle, following driving based on a following distance, maintenance of a vehicle speed of driving, warning of a vehicle collision, warning of deviation of the vehicle from a lane, and the like. In addition, the microcomputer 7610 can perform cooperative control for automatic driving by controlling the driving force generation device, the steering mechanism, the braking device, and the like on the basis of obtained information about the surroundings of the vehicle, which makes the vehicle autonomously travel without depending on an operation of a driver or the like.

[0499] The microcomputer 7610 can generate three-dimensional distance information between the vehicle and an object such as a surrounding structure, a person, or the like on the basis of information obtained via at least one of the general-purpose communication I / F 7620, the dedicated communication I / F 7630, the positioning section 7640, the beacon receiving section 7650, the in-vehicle device I / F 7660, and the in-vehicle network I / F 7680, and generate local map information including information about the surroundings of the current position of the vehicle. Furthermore, the microcomputer 7610 can predict a danger such as a collision of the vehicle, approach of a pedestrian, or the like, entry into a closed road, and the like on the basis of the obtained information, and generate a warning signal. The warning signal may, for example, be a signal for generating a warning sound or lighting a warning lamp.

[0500] The sound / image output section 7670 transmits an output signal of at least one of a sound or an image to an output device capable of visually or aurally notifying information to an occupant of the vehicle or outside of the vehicle. The output device may, for example, be a speaker or a display. Figure 52In the example of , the audio speaker 7710, the display unit 7720, and the instrument panel 7730 are shown as output devices. For example, the display unit 7720 may include at least one of an onboard display and a head-up display. The display unit 7720 may have an augmented reality (AR) display function. The output device may be different from these devices and may be another device such as headphones, a wearable device such as a glasses-type display worn by a passenger, a projector, a lamp, or the like. In the case where the output device is a display device, the display device visually displays the results obtained by the various processes performed by the microcomputer 7610 or information received from another control unit in various forms such as text, images, tables, graphics, etc. In addition, in the case where the output device is an audio output device, the audio output device converts an audio signal composed of reproduced audio data or sound data, etc. into an analog signal and outputs the analog signal audibly.

[0501] By the way, through Figure 52 At least two control units connected to each other by the communication network 7010 in the example shown can be integrated into one control unit. Alternatively, each individual control unit may include multiple control units. In addition, the vehicle control system 7000 may include another control unit not shown in the figure. In addition, part or all of the functions performed by one of the control units described above can be assigned to another control unit. That is, as long as information is sent and received via the communication network 7010, predetermined arithmetic processing can be performed by any control unit. Similarly, a sensor or device connected to one of the control units can be connected to another control unit, and multiple control units can send and receive detection information to each other via the communication network 7010.

[0502] The above describes an example of a vehicle control system to which the technology of the present disclosure can be applied. In the technology of the present disclosure, for example, when the imaging unit 7410 includes a ToF camera (ToF sensor) among the aforementioned components, the light receiving device according to the first or second embodiment can be used as the ToF camera. For example, by installing the light receiving device as a ToF camera in a distance measuring device, a vehicle control system capable of highly accurate detection of the measurement object can be constructed.

[0503] <Configurations that the present disclosure can take>

[0504] It should be noted that the present disclosure may also have the following configurations.

[0505] <<A. 光接收装置> >

[0506] [A-1] A light receiving device,

[0507] include:

[0508] a light receiving unit having a plurality of photon counting type light receiving elements that receive light from an object;

[0509] an adding unit configured to add values of a plurality of the light receiving elements at a predetermined time to use a result as a pixel value; and

[0510] a logarithmic transformation processing unit configured to transform a pixel value obtained as a result of the addition by the adding unit into a logarithmic value or an approximate value thereof to use the obtained value as logarithmic representation data for a distance measurement calculation; wherein

[0511] receive reflected light from an object to be measured based on pulsed light applied by a light source unit.

[0512] [A-2] The light receiving apparatus according to the above-mentioned [A-1], wherein

[0513] the logarithmic transformation processing unit transforms a value obtained by subtracting a predetermined value from the pixel value into a logarithmic value or an approximate value thereof to use the obtained value as the logarithmic representation data for the distance measurement calculation.

[0514] [A-3] The light receiving apparatus according to the above-mentioned [A-2], wherein

[0515] in a case where the predetermined value is larger than the pixel value, the logarithmic transformation processing unit performs transformation processing with a value obtained as a result of the subtraction being zero (0).

[0516] [A-4] The light receiving apparatus according to the above-mentioned [A-3], further comprising

[0517] assuming that the predetermined value is an ambient light intensity estimation value obtained by adding a predetermined addend to a value obtained by multiplying an arithmetic mean value of ambient light by a predetermined multiplier;

[0518] an ambient light estimation processing unit configured to calculate the arithmetic mean value of the ambient light in a logarithmic representation based on the pixel value to estimate an ambient light intensity; wherein

[0519] the logarithmic transformation processing unit subtracts the ambient light intensity estimated by the ambient light estimation processing unit from the pixel value.

[0520] [A-5] The light receiving apparatus according to the above-mentioned [A-1], wherein

[0521] The logarithmic conversion processing unit subtracts data obtained as a result of conversion from a predetermined value to a logarithmic value or an approximate value thereof from data obtained as a result of conversion from the pixel value to a logarithmic value or an approximate value thereof, and uses the resultant data as the logarithmic representation data for range-finding calculation.

[0522] [A-6] The light-receiving device according to the above-mentioned [A-5], further comprising,

[0523] The predetermined value is assumed to be an ambient light intensity estimate obtained by adding a predetermined addend to a value obtained by multiplying a geometric mean value of ambient light by a predetermined multiplier;

[0524] an ambient light estimation processing unit configured to calculate the geometric mean value of the ambient light in a logarithmic representation based on the pixel value to estimate an ambient light intensity; wherein

[0525] The logarithmic conversion processing unit converts the ambient light intensity estimated by the ambient light estimation processing unit to a logarithmic value or an approximate value thereof.

[0526] [A-7] The light-receiving device according to any one of the above-mentioned [A-2] to [A-6], further comprising:

[0527] a histogram addition processing unit configured to associate a time of flight from emission of pulsed light applied by the light source unit to return of reflected light with a group number of a histogram, and store logarithmic representation data calculated based on pixel values sampled at each time as a count value of the group number corresponding to the time.

[0528] [A-8] The light-receiving device according to the above-mentioned [A-7], wherein

[0529] The histogram addition processing unit adds and updates the histogram the logarithmic representation data at each time from the reflection of the reflected light from the object under test based on emission of the pulsed light applied by the light source unit multiple times to the count value of the group number corresponding to the time.

[0530] [A-9] The light-receiving device according to the above-mentioned [A-8], wherein

[0531] The histogram addition processing unit generates a histogram obtained by accumulating count values calculated from pixel values obtained by receiving the reflected light based on emission of the pulsed light applied by the light source unit multiple times.

[0532] [A-10] The light-receiving device according to the above-mentioned [A-8], wherein

[0533] The histogram addition processing unit subtracts a value calculated from pixel values sampled over a plurality of times in a predetermined measurement period as the predetermined value from the pixel values, and adds the count values of the groups of the histogram calculated by the subtraction as the logarithmic representation data.

[0534] [A-11] The light-receiving device according to any one of the above-mentioned [A-1] to [A-10], further comprising:

[0535] a reflected light detection unit configured to detect a peak value of each reflected light by performing amplitude comparison between count values of histograms using logarithmic representation, and calculate a distance based on a time corresponding to a group number at a rising start of the peak value.

[0536] [A-12] The light-receiving device according to any one of the above-mentioned [A-1] to [A-11], wherein,

[0537] an ambient light estimation processing unit,

[0538] calculating an approximation value S of a logarithmic value of a sum of pixel values while maintaining a logarithmic representation of logarithmic representation data LogD obtained by transforming pixel values sampled at a plurality of times in a predetermined measurement period into a logarithmic value or an approximation value of a logarithmic value using a predetermined approximation expression;

[0539] calculating an approximation value μ of an arithmetic mean value from a value obtained by subtracting a logarithmic value of the number N of samplings or an approximation value thereof from the approximation value S;

[0540] calculating an approximation value SS of a logarithmic value of a sum obtained by squaring the pixel values while maintaining a logarithmic representation of a value obtained by doubling the logarithmic representation data LogD using a predetermined approximation expression;

[0541] calculating a value MM obtained by subtracting a logarithmic value of the number N of samplings or an approximation value thereof from the approximation value SS;

[0542] calculating an approximation value V of a variance of the ambient light by using the approximation value μ of the arithmetic mean value and the value MM; and

[0543] outputting an ambient light intensity estimation value obtained by adding a predetermined addend to a value obtained by multiplying the approximation value μ of the arithmetic mean value by a predetermined multiplier, and an approximation value of a standard deviation of the ambient light calculated from the approximation value V of the variance.

[0544] [A-13] The light-receiving device according to any one of the above-mentioned [A-1] to [A-12], wherein,

[0545] The ambient light estimation processing unit transforms a sum obtained by summing pixel values sampled over a plurality of times in a predetermined measurement period into a logarithmic value or an approximation thereof, and outputs an image in which the transformed logarithmic representation data is used as the pixel values.

[0546] [A-14] The light-receiving apparatus according to any one of the above-mentioned [A-1] to, wherein

[0547] The ambient light estimation processing unit calculates an approximation of a logarithmic value of a sum of pixel values while maintaining a logarithmic representation of logarithmic representation data obtained by transforming pixel values sampled over a plurality of times in a predetermined measurement period into a logarithmic value or an approximation of a logarithmic value using a predetermined approximation expression, and outputs an image in which the approximation is used as the pixel values.

[0548] [A-15] The light-receiving apparatus according to any one of the above-mentioned [A-1] to, further comprising:

[0549] A logarithmic transformation unit configured to further logarithmically transform and compress the cumulative histogram of the logarithmic representation.

[0550] [A-16] The light-receiving apparatus according to any one of the above-mentioned [A-1] to, further comprising:

[0551] A logarithmic transformation unit configured to further logarithmically transform and compress the cumulative histogram of the logarithmic representation after subtracting a minimum value of the cumulative histogram.

[0552] [A-17] The light-receiving apparatus according to any one of the above-mentioned [A-1] to, wherein

[0553] The histogram addition processing unit has a data compression / decompression function by differential encoding before and after storing the logarithmic representation data in a memory.

[0554] [A-18] The light-receiving apparatus according to any one of the above-mentioned [A-1] to, wherein

[0555] The light-receiving element includes an avalanche photodiode operated in a Geiger mode.

[0556] <<B. Signal processing method for light-receiving apparatus>>

[0557] [B-1] A signal processing method for a light-receiving apparatus,

[0558] The light-receiving apparatus includes:

[0559] A light-receiving unit having a plurality of photon counting type light-receiving elements that receive light from an object; and

[0560] The light receiving device receives reflected light from the object to be measured based on the pulse light applied by the light source unit, and the signal processing method includes:

[0561] In the signal processing on the optical receiving device,

[0562] adding values ​​of a plurality of said light receiving elements at a predetermined time and using the result as a pixel value; and

[0563] Next, the pixel values ​​are converted into logarithmic values ​​or approximate values ​​thereof to use the result as logarithmic representation data for distance measurement calculation.

[0564] <<C.距离测量装置> >

[0565] [C-1] A distance measuring device,

[0566] include:

[0567] a light source unit configured to apply pulsed light to the object to be measured; and

[0568] A light receiving device is configured to receive reflected light from the object to be measured based on the pulse light applied by the light source unit; wherein,

[0569] The light receiving device comprises:

[0570] a light receiving unit having a plurality of photon counting type light receiving elements that receive light from a subject;

[0571] an adding unit configured to add values ​​of a plurality of the light receiving elements at a predetermined time and use the result as a pixel value; and

[0572] A logarithmic conversion processing unit is configured to convert the pixel value obtained as a result of the addition by the adding unit into a logarithmic value or an approximate value thereof to use the resultant value as logarithmic representation data for distance measurement calculation.

[0573] [C-2] The distance measuring device according to [C-1] above, wherein:

[0574] The logarithmic conversion processing unit converts a value obtained by subtracting a predetermined value from the pixel value into a logarithmic value or an approximate value thereof to use the resultant value as the logarithmic representation data for distance measurement calculation.

[0575] [C-3] The distance measuring device according to [C-2] above, wherein:

[0576] In a case where the predetermined value is greater than the pixel value, the logarithmic transform processing unit performs transform processing with a value obtained as a result of subtraction being zero (0).

[0577] [C-4] The distance measuring device according to the above [C-3], further comprising:

[0578] assuming that the predetermined value is an ambient light intensity estimation value obtained by adding a predetermined addend to a value obtained by multiplying an arithmetic mean value of ambient light by a predetermined multiplier;

[0579] an ambient light estimation processing unit configured to calculate the arithmetic mean value of the ambient light in a logarithmic representation based on the pixel values to estimate an ambient light intensity; wherein

[0580] the logarithmic transformation processing unit subtracts the ambient light intensity estimated by the ambient light estimation processing unit from the pixel values.

[0581] [C-5] The distance measuring device according to the above [C-1], wherein

[0582] the logarithmic transformation processing unit subtracts data obtained as a result of transforming a predetermined value into a logarithmic value or an approximate value thereof from data obtained as a result of transforming the pixel values into logarithmic values or approximate values thereof, and uses the resultant data as the logarithmic representation data for distance measurement calculation.

[0583] [C-6] The distance measuring device according to the above [C-5], further comprising:

[0584] assuming that the predetermined value is an ambient light intensity estimation value obtained by adding a predetermined addend to a value obtained by multiplying a geometric mean value of ambient light by a predetermined multiplier;

[0585] an ambient light estimation processing unit configured to calculate the geometric mean value of the ambient light in a logarithmic representation based on the pixel values to estimate an ambient light intensity; wherein

[0586] the logarithmic transformation processing unit transforms the ambient light intensity estimated by the ambient light estimation processing unit into a logarithmic value or an approximate value thereof.

[0587] [C-7] The distance measuring device according to any one of the above [C-2] to [C-6], further comprising:

[0588] a histogram addition processing unit configured to associate a time of flight from emission to return of reflected light of pulsed light applied by the light source unit with a group number of a histogram and store a logarithmic representation data calculated based on pixel values sampled at each time as a count value of the group number corresponding to the time.

[0589] [C-8] The distance measuring device according to the above [C-7], wherein

[0590] The histogram addition processing unit adds the logarithmic representation data of the reflected light from the object to be measured based on the emission of the pulse light applied multiple times by the light source unit to the count value corresponding to the number of groups at the time and updates the histogram.

[0591] [C-9] The distance measuring device according to [C-8] above, wherein:

[0592] The histogram addition processing unit generates a histogram obtained by accumulating count values ​​calculated from pixel values ​​obtained by receiving the reflected light based on emission of the pulse light applied a plurality of times by the light source unit.

[0593] [C-10] The distance measuring device according to [C-8] above, wherein:

[0594] The histogram addition processing unit subtracts a value calculated using pixel values ​​sampled at a plurality of times in a predetermined measurement period from the pixel value as the predetermined value, and adds logarithmic representation data calculated by the subtraction as the count value of the group number of the histogram.

[0595] [C-11] The distance measuring device according to any one of [C-1] to [C-1], further comprising:

[0596] The reflected light detection unit is configured to detect a peak value of each reflected light by performing amplitude comparison between count values ​​of a histogram expressed using a logarithm, and calculate a distance based on a time corresponding to a group number when a rise of the peak value starts.

[0597] [C-12] The distance measuring device according to any one of [C-1] to [C-1] above,

[0598] Ambient light estimation processing unit,

[0599] calculating an approximate value S of the logarithmic value of the sum of the pixel values ​​while maintaining the logarithmic representation of the logarithmic representation data LogD, wherein the logarithmic representation data LogD is obtained by converting the pixel values ​​sampled at a plurality of times in a predetermined measurement period into logarithmic values ​​or approximate values ​​of the logarithmic values ​​using a predetermined approximate expression;

[0600] calculating an approximate value μ of the arithmetic mean from a value obtained by subtracting a logarithmic value of the number of samples N or an approximate value thereof from the approximate value S;

[0601] calculating an approximate value SS of a logarithmic value of a sum obtained by squaring pixel values ​​while maintaining a logarithmic representation of a value obtained by doubling logarithmic representation data LogD using a predetermined approximate expression;

[0602] calculating a value MM obtained by subtracting a logarithmic value of the number N of samples or an approximation thereof from the approximation SS;

[0603] calculating an approximation V of the variance of the ambient light by using the approximation μ of the arithmetic mean value and the value MM; and

[0604] outputting an ambient light intensity estimation value obtained by adding a predetermined addend to a value obtained by multiplying the approximation μ of the arithmetic mean value by a predetermined multiplier, and an approximation of the standard deviation of the ambient light calculated based on the approximation V of the variance.

[0605] [C-13] The distance measuring apparatus according to any one of the above-mentioned [C-1] to, wherein

[0606] The ambient light estimation processing unit transforms a sum obtained by summing pixel values sampled at a plurality of times in a predetermined measurement period into a logarithmic value or an approximation thereof, and outputs an image in which the transformed logarithmic representation data is used as the pixel values.

[0607] [C-14] The distance measuring apparatus according to any one of the above-mentioned [C-1] to, wherein

[0608] The ambient light estimation processing unit calculates an approximation of a logarithmic value of the sum of the pixel values while maintaining a logarithmic representation of the logarithmic representation data obtained by transforming the pixel values sampled at a plurality of times in a predetermined measurement period into a logarithmic value or an approximation thereof using a predetermined approximation expression, and outputs an image in which the approximation is used as the pixel values.

[0609] [C-15] The distance measuring apparatus according to any one of the above-mentioned [C-1] to, further comprising:

[0610] a logarithmic transformation unit configured to further logarithmically transform and compress the cumulative histogram of the logarithmic representation.

[0611] [C-16] The distance measuring apparatus according to any one of the above-mentioned [C-1] to, further comprising:

[0612] a logarithmic transformation unit configured to further logarithmically transform and compress the cumulative histogram of the logarithmic representation after subtracting a minimum value of the cumulative histogram.

[0613] [C-17] The distance measuring apparatus according to any one of the above-mentioned [C-1] to, wherein

[0614] The histogram addition processing unit has a data compression / decompression function by differential encoding before and after storing the logarithmic representation data in a memory.

[0615] [C-18] The distance measuring apparatus according to any one of [C-l] to [C-17] described above, wherein

[0616] The light-receiving element includes an avalanche photodiode operated in a Geiger mode.

[0617] LIST OF FIGURE NUMBERS

[0618] 1 distance measuring apparatus

[0619] 10 object to be measured

[0620] 20 light source unit

[0621] 30 light-receiving device

[0622] 31 control unit

[0623] 32 light-receiving unit

[0624] 33 adding unit

[0625] 34 histogram adding processing unit

[0626] 35 ambient light estimation processing unit

[0627] 36 smoothing filter

[0628] 37 reflected light detection unit

[0629] 38 external output interface (I / F)

[0630] 40 host

[0631] 50 SPAD pixel

[0632] 60 pixel

[0633] 61 logarithmic conversion processing unit

[0634] 62 logarithmic representation ambient light estimation processing unit

[0635] 63 logarithmic representation histogram adding processing unit

[0636] 64 logarithmic representation smoothing filter

[0637] 65 logarithmic conversion unit

[0638] 66 logarithmic representation reflected light detection unit

[0639] 70 pixel group

Claims

1. A light receiving device, comprising: a light receiving unit having a plurality of photon counting type light receiving elements that receive light from a subject; an adding unit configured to add values ​​of a plurality of the light receiving elements at a predetermined time and use the result as a pixel value; as well as a logarithmic conversion processing unit configured to convert the pixel value obtained as a result of the addition by the adding unit into a logarithmic value to use the obtained value as logarithmic representation data for distance measurement calculation; wherein, The light receiving device is configured to perform the distance measurement calculation based on the logarithmic representation data, in, The logarithmic conversion processing unit subtracts second data from first data, which is a result of converting the pixel value into a logarithmic value, and uses the resulting data as the logarithmic representation data for distance measurement calculation, wherein the first data is a result of converting the pixel value into a logarithmic value, and the second data is a result of converting a predetermined value into a logarithmic value. The light receiving device further comprises: Assuming that the predetermined value is an estimated value of the ambient light intensity obtained by adding a predetermined addend to a value obtained by multiplying a geometric mean of the ambient light by a predetermined multiplier; an ambient light estimation processing unit configured to calculate the geometric mean of the ambient light in logarithmic representation based on the pixel values ​​to estimate the ambient light intensity; wherein, The logarithmic conversion processing unit converts the ambient light intensity estimated by the ambient light estimation processing unit into a logarithmic value.

2. The optical receiving device according to claim 1, further comprising: A histogram addition processing unit is configured to associate the flight time from the emission of pulsed light applied by the light source unit to the object to the return of light reflected from the object with the number of groups of the histogram, and to store logarithmic representation data calculated based on the pixel values ​​sampled at each time as a count value corresponding to the number of groups of the time.

3. The light receiving device according to claim 2, wherein The histogram addition processing unit adds the logarithmic representation data of the reflected light from the object to be measured based on the emission of the pulse light applied multiple times by the light source unit to the count value of the group number corresponding to the time and updates the histogram.

4. The light receiving device according to claim 3, wherein The histogram addition processing unit generates a histogram obtained by accumulating count values ​​calculated from pixel values ​​obtained by receiving the reflected light based on emission of the pulse light applied a plurality of times by the light source unit.

5. The light receiving device according to claim 3, wherein The histogram addition processing unit subtracts a value calculated using pixel values ​​sampled at a plurality of times in a predetermined measurement period from the pixel value as the predetermined value, and adds logarithmic representation data calculated by the subtraction as the count value of the group number of the histogram.

6. The optical receiving device according to claim 1, further comprising: The reflected light detection unit is configured to detect a peak value of each reflected light by performing amplitude comparison between count values ​​of a histogram expressed using a logarithm, and calculate a distance based on a time corresponding to a group number when a rise of the peak value starts.

7. The optical receiving device according to claim 1, further comprising: The logarithmic transformation unit is configured to further perform logarithmic transformation and compress the cumulative histogram represented by the logarithm.

8. The optical receiving device according to claim 1, further comprising: The logarithmic transformation unit is configured to further logarithmically transform and compress the logarithmically represented cumulative histogram after subtracting the minimum value of the cumulative histogram.

9. The light receiving device according to claim 1, wherein The histogram addition processing unit has a data compression / decompression function by differential coding before and after the memory storing the logarithmic representation data.

10. The light receiving device according to claim 1, wherein The light receiving element includes an avalanche photodiode operating in a Geiger mode.

11. A signal processing method for the optical receiving device according to claim 1, The signal processing method comprises: receiving light from the object; adding values ​​of a plurality of said light receiving elements at a predetermined time and using the result as a pixel value; and converting the pixel value obtained as a result of the addition into a logarithmic value, subtracting second data obtained as a result of converting a predetermined value into a logarithmic value from first data obtained as a result of converting the pixel value into a logarithmic value, to use the result as logarithmically expressed data for distance measurement calculation; as well as performing said ranging calculation based on said logarithmic representation data, Further including: Assuming that the predetermined value is an ambient light intensity estimation value obtained by adding a predetermined addend to a value obtained by multiplying a geometric mean of ambient light by a predetermined multiplier, calculating the geometric mean of the ambient light in logarithmic representation based on the pixel values ​​to estimate the ambient light intensity; The estimated ambient light intensity is converted into a logarithmic value.

12. A distance measuring device, include: a light source unit configured to apply pulsed light to the object to be measured; and A light receiving device is configured to receive reflected light from the object to be measured based on the pulse light applied by the light source unit; wherein, The light receiving device comprises: a light receiving unit having a plurality of photon counting type light receiving elements that receive light from a subject; an adding unit configured to add values ​​of a plurality of the light receiving elements at a predetermined time and use the result as a pixel value; and a logarithmic conversion processing unit configured to convert the pixel value obtained as a result of the addition by the adding unit into a logarithmic value to use the obtained value as logarithmic representation data for distance measurement calculation, wherein the light receiving device is configured to perform the distance measurement calculation based on the logarithmic representation data, in, The logarithmic conversion processing unit subtracts second data from first data, which is a result of converting the pixel value into a logarithmic value, and uses the resulting data as the logarithmic representation data for distance measurement calculation, wherein the first data is a result of converting the pixel value into a logarithmic value, and the second data is a result of converting a predetermined value into a logarithmic value. The light receiving device further comprises: Assuming that the predetermined value is an estimated value of the ambient light intensity obtained by adding a predetermined addend to a value obtained by multiplying a geometric mean of the ambient light by a predetermined multiplier; an ambient light estimation processing unit configured to calculate the geometric mean of the ambient light in logarithmic representation based on the pixel values ​​to estimate the ambient light intensity; wherein, The logarithmic conversion processing unit converts the ambient light intensity estimated by the ambient light estimation processing unit into a logarithmic value.

Images