JP3906858B2 - Distance image sensor - Google Patents

Description

  The present invention relates to a distance image sensor that captures an image of a target space and generates a distance image having a pixel value as a distance to a target existing in the target space.

  Conventionally, the three-dimensional information of the target space is obtained by scanning the light in the target space, receiving the reflected light from the target object in the target space, and determining the distance to the target using the principle of triangulation. A ranging sensor that can be obtained has been proposed (see, for example, Patent Document 1).

  However, since it is necessary to scan light in the target space in order to obtain the three-dimensional information of the target space with the distance measuring sensor based on the principle of the triangulation method, it is relatively long until the three-dimensional information is obtained for the entire target space. There is a problem that it takes time and cannot be used in an application such as tracking a moving object.

In order to solve this kind of problem, and irradiates the object space the light modulated-strength, captures an image of the object space, the object in the object space using the phase difference between the time of light projecting and when receiving Previously proposed a distance image sensor that can obtain a distance up to (for example, see Patent Document 2) .
JP-A-9-257418 JP 2004-45304 A

  By the way, the distance image sensor described above uses a light detection element in which a plurality of photosensitive portions that image the target space are arranged, and is based on the received light amount in the light receiving period synchronized with the phase of intensity modulation of the light irradiated to the target space. Finding the distance to the object. In addition, the light receiving period is set to a time shorter than one period of the modulation signal, and the electric charge generated in the photosensitive portion is taken out from the light detection element every detection period of one period or more of the modulation signal, and the distance is calculated. Is going.

  In order to reduce the influence of shot noise generated in the photosensitive part and increase the SN ratio, it is desirable to increase the amount of received light by setting the detection period to a long period. In an environment where light components are included and a large amount of external light components are included, the light detection element is likely to be saturated by increasing the detection period. When the photodetection element is saturated, the amount of light received by the photosensitive portion becomes irrelevant to the intensity-modulated light, which causes a problem that the distance cannot be accurately obtained for the pixel corresponding to the photosensitive portion. On the other hand, if the detection period is shortened, the photodetection element is less likely to be saturated. However, as described above, the SN ratio decreases, and if the SN ratio decreases extremely, the distance cannot be obtained accurately.

  The present invention has been made in view of the above-mentioned reasons, and an object of the present invention is to provide a distance image sensor that improves the distance measurement accuracy so as to obtain a high S / N ratio while preventing saturation of the light detection element. There is to do.

According to the first aspect of the present invention, a light source that irradiates the target space with light that has been intensity-modulated with a modulation signal having a predetermined period, and a plurality of light sources that receive light from the target space and generate charges corresponding to the received light amount A light detection element that has a photosensitive part and images a target space, a control circuit part that controls a light receiving period in which each photosensitive part receives light from the target space, and an object using charges generated in the photosensitive part An image generation unit that generates a distance image using the distance as a pixel value, the light receiving period is set to be synchronized with the phase of the modulation signal and shorter than the period of the modulation signal, A plurality of adjacent photosensitive portions are used as calculation units, and charge obtained by collecting charges obtained in a plurality of light receiving periods for each detection period that is a period of one or more periods of the modulation signal is given to the image generation unit , and each calculation unit The light receiving period of the photosensitive unit is set to the detection period. Transfer timing of the charge so as to change to a different light receiving period of the phase ones of the phase are controlled by the control circuit unit, the image generating unit, using the amount of charge accumulated by the light receiving period the amount of charge of a plurality of detection periods the distance And the distance is used as the pixel value of the distance image .

In the invention of claim 2, prior Symbol image generation unit, in a plurality of detection periods for accumulating charges obtained by the respective photosensitive portions to be operated units, in equal number to the number of the light receiving period for each detection period and characterized in that it.

According to the configuration of the present invention, since the charge is delivered from the light detection element to the image generation unit every certain detection period, the amount of charge accumulated in the light detection element can be relatively reduced, and saturation of the light detection element can be achieved. In addition, since the image generation unit obtains the distance using the charge amount obtained by integrating the charges for a plurality of detection periods, the image generation unit is less affected by shot noise, and a high SN ratio is obtained. There is an advantage that the distance can be measured with high accuracy. In addition, the light receiving period of each photosensitive unit, which is a calculation unit, is changed to a light receiving period having a different phase among the phases for each detection period, and the charge amount obtained by integrating the charge amounts of a plurality of detection periods for each light receiving period is calculated. Since the distance is obtained by using this, even if the different photosensitive sections within the detection period receive light during the light receiving period synchronized with the different phases of the modulation signal, the amount of charge accumulated for obtaining the distance is an arithmetic unit. The positional information of the plurality of photosensitive portions is not included, and the reliability of the obtained distance is increased.

  First, the basic configuration of the distance image sensor used in this embodiment will be described. As shown in FIG. 1, the distance image sensor includes a light emitting source 2 that irradiates light to a target space, and receives a light from the target space and obtains an electrical output having an output value that reflects the amount of received light. 1 is provided. The distance to the object Ob existing in the object space is the time from when the light is emitted from the light source 2 to the object space until the reflected light from the object Ob enters the light detection element 1 (“flight time”). Call). However, since the flight time is very short, use the intensity-modulated light that is modulated so that the intensity of the light irradiating the target space changes periodically at a constant period, and use the phase when the intensity-modulated light is received. Ask for time.

As shown in FIG. 2A, if the intensity of light radiated from the light source 2 into the space changes as shown by curve A, and the amount of received light received by the light detecting element 1 changes as shown by curve B, Since the phase difference ψ corresponds to the time of flight, the distance to the object Ob can be obtained by obtaining the phase difference ψ. Further, the phase difference ψ can be calculated using the received light amount of the curve B obtained at a plurality of timings of the curve A. For example, it is assumed that the received light amounts of curve B obtained with the phases of curve A at 0, 90, 180, and 270 degrees are A0, A1, A2, and A3 (received light amounts A0, A1, A2,. A3 is indicated by hatching). However, the received light quantity A0, A1, A2, A3 in each phase is not an instantaneous value but a received light quantity integrated over a predetermined light receiving period Tw. Now, while obtaining the received light amounts A0, A1, A2, and A3, the phase difference ψ does not change (that is, the distance to the object Ob does not change), and the reflectance of the object Ob does not change. Shall. Further, it is assumed that the intensity of light emitted from the light emitting source 2 is modulated by a sine wave, and the intensity of light received by the light detection element 1 at time t is represented by A · sin (ωt + δ) + B. Here, A is the amplitude, B is the DC component (the average value of the external light component and the reflected light component), ω is the angular frequency, and δ is the initial phase. The received light amounts A0, A1, A2, and A3 received by the light detection element 1 are set to instantaneous values, not integrated values of the light receiving period Tw, and time t = n / f (n = 0, 1, 2, synchronized with the period of the modulation signal) ,...) Is set to A0 = A · sin (δ) + B, the received light amounts A0, A1, A2, and A3 can be expressed as follows. The reflected light component means a component of light emitted from the light source 2 and incident on the light detection element 1 after being reflected by the object Ob.
A0 = A · sin (δ) + B
A1 = A · sin (π / 2 + δ) + B
A2 = A · sin (π + δ) + B
A3 = A · sin (3π / 2 + δ) + B
Since the phase difference is ψ in FIG. 2, the initial phase δ (phase at time t = 0) of the waveform related to the amount of received light of the light detection signal 1 is −ψ. That is, since δ = −ψ, A0 = −A · sin (ψ) + B, A1 = A · cos (ψ) + B, A2 = A · sin (ψ) + B, A3 = −A · cos (ψ) As a result, the relationship between each received light quantity A0, A1, A2, A3 and the phase difference ψ is expressed by the following equation.
ψ = tan ⁻¹ {(A2−A0) / (A1−A3)} (1)
In equation (1), the instantaneous values of the received light amounts A0, A1, A2, and A3 are used. However, even if the integrated values in the light receiving period Tw are used as the received light amounts A0, A1, A2, and A3, the phase difference in equation (1) ψ can be obtained.

Further, when the intensity of light received by the light detection element 1 is A · cos (ωt + δ) + B, that is, time t = n / f (n = 0, 1, 2,...) Synchronized with the period of the modulation signal. If the received light quantity at is A0 = A · cos (δ) + B, the phase difference ψ can be obtained by the following equation.
ψ = tan ⁻¹ {(A1−A3) / (A0−A2)}
This relationship is a relationship in which the timing for synchronizing with the modulation signal is shifted by 90 degrees. In addition, since the sign of the distance value is positive, if the sign is negative when the phase difference ψ is obtained, the order of the denominator in the parenthesis of tan ⁻¹ or each term of the numerator is changed, or An absolute value may be used.

  As described above, in order to modulate the intensity of the light irradiated to the target space, the light source 2 includes, for example, a structure in which a large number of light emitting diodes are arranged on one plane, a combination of a semiconductor laser and a diverging lens, or the like. Is used. The light source 2 is driven by a modulation signal having a predetermined modulation frequency output from the control circuit unit 3, and the intensity of the light emitted from the light source 2 is modulated by the modulation signal. The control circuit unit 3 modulates the intensity of light emitted from the light source 2 with, for example, a 20 MHz sine wave. The intensity of the light emitted from the light source 2 may be modulated by a triangular wave, a sawtooth wave or the like in addition to the modulation by a sine wave. In short, any configuration is acceptable as long as the intensity is modulated at a constant period. May be adopted.

  The light detection element 1 includes a plurality of photosensitive portions 11 regularly arranged. A light receiving optical system 5 is disposed in the light incident path to the photosensitive portion 11. The photosensitive unit 11 is a part where light from the target space is incident through the light receiving optical system 5 in the light detection element 1, and the photosensitive unit 11 generates an amount of charge corresponding to the amount of received light. Further, the photosensitive portions 11 are arranged on the lattice points of the planar lattice, and are arranged in a matrix in which, for example, a plurality are arranged at equal intervals in the vertical direction (that is, the vertical direction) and the horizontal direction (that is, the horizontal direction). Is done.

  The light receiving optical system 5 associates the line-of-sight direction when viewing the target space from the light detection element 1 with each photosensitive portion 11. That is, the range in which light enters each photosensitive portion 11 through the light receiving optical system 5 can be regarded as a conical field of view with a small apex angle set for each photosensitive portion 11 with the center of the light receiving optical system 5 as the apex. . Therefore, if the reflected light emitted from the light emitting source 2 and reflected by the object Ob existing in the target space enters the photosensitive unit 11, the optical axis of the light receiving optical system 5 depends on the position of the photosensitive unit 11 that has received the reflected light. Can be known as the reference direction.

  Since the light receiving optical system 5 is generally arranged so that the optical axis is orthogonal to the plane on which the photosensitive portions 11 are arranged, the center of the light receiving optical system 5 is the origin, and the vertical and horizontal directions of the plane on which the photosensitive portions 11 are arranged If an orthogonal coordinate system is set in which the optical axis of the light receiving optical system 5 is in the direction of three axes, the angle (so-called azimuth and elevation) when the position of the object Ob existing in the target space is expressed in spherical coordinates is set. It corresponds to each photosensitive portion 11. The light receiving optical system 5 can also be arranged so that the optical axis intersects at an angle other than 90 degrees with respect to the plane on which the photosensitive portions 11 are arranged.

  In the present embodiment, as described above, in order to obtain the distance to the object Ob, the received light amounts A0, A1, and A2 are synchronized at four timings synchronized with the intensity change of the light emitted from the light source 2 to the target space. , A3. Therefore, it is necessary to control the timing to obtain the desired received light amount A0, A1, A2, A3. In addition, since the amount of charge generated in the photosensitive portion 11 is small in one cycle of the intensity change of light irradiated from the light source 2 to the target space, it is desirable to accumulate the charges over a plurality of cycles. Therefore, as shown in FIG. 1, a plurality of charge accumulating units 13 for accumulating the charges generated in the respective photosensitive units 11 are provided, and the areas of the regions for generating the charges that can be used in the respective photosensitive units 11 are changed to change the respective areas. A plurality of sensitivity control units 12 for adjusting the sensitivity of the photosensitive unit 11 are provided.

  In each sensitivity control unit 12, the sensitivity of the photosensitive unit 11 corresponding to the sensitivity control unit 12 is increased at any one of the four points described above, and in the photosensitive unit 11 with increased sensitivity, the received light amount A0, Since charges corresponding to A1, A2, and A3 are mainly generated, charges corresponding to the received light amounts A0, A1, A2, and A3 can be accumulated in the charge accumulating unit 13 corresponding to the photosensitive unit 11.

  By the way, the sensitivity control unit 12 changes the amount of charge generated in each period by changing the area (substantial light receiving area) of the region that generates the charge that can be used in the photosensitive unit 11. The charges accumulated in 13 include not only the charges generated during the period in which the received light amounts A0, A1, A2, and A3 are obtained, but also the charges generated during other periods. Now, in the sensitivity control unit 12, the sensitivity of a period for generating charges corresponding to the received light amounts A 0, A 1, A 2, A 3 (hereinafter referred to as “light reception period”) is α, and the other period (hereinafter, “ It is assumed that the sensitivity of the “holding period” is β, and the photosensitive portion 11 generates a charge proportional to the amount of received light. Under this condition, the charge accumulating unit 13 that accumulates charges corresponding to the received light amount A0 is proportional to αA0 + β (A1 + A2 + A3) + βAx (Ax is the received light amount other than the period during which the received light amounts A0, A1, A2, and A3 are obtained). In the charge accumulating unit 13 that accumulates charges and accumulates charges corresponding to the received light quantity A2, charges proportional to αA2 + β (A0 + A1 + A3) + βAx are accumulated. As described above, when obtaining the phase difference ψ, (A2−A0) is obtained, and A2−A0 = (α−β) (A2−A0), and similarly, A1−A3 = (α−). β) Since (A1-A3), (A2-A0) / (A1-A3) theoretically has the same value regardless of the presence or absence of charge mixing. The phase difference ψ has the same value.

  The photodetecting element 1 including the photosensitive unit 11, the sensitivity control unit 12, and the charge accumulating unit 13 is configured as one semiconductor device, and the photodetecting element 1 transmits charges accumulated in the charge accumulating unit 13 to the outside of the semiconductor device. A charge extraction unit 14 is provided for extraction. The charge extraction unit 14 has the same configuration as the vertical transfer unit and horizontal transfer unit in the CCD image sensor.

  The electric charge extracted from the electric charge extraction unit 14 is given to the image generation unit 4 as an image signal (electrical output), and the distance to the object Ob in the target space in the image generation unit 4 is calculated using the above-described equation (1). It is calculated from the received light quantity A0, A1, A2, A3. That is, the image generation unit 4 calculates the distance to the object Ob in each direction corresponding to each photosensitive unit 11, and calculates the three-dimensional information of the target space. By using this three-dimensional information, it is possible to generate a distance image in which the pixel values of the pixels matching each direction of the target space are distance values.

  Hereinafter, a specific structural example of the light detection element 1 will be described. The photodetecting element 1 shown in FIG. 3 includes a plurality of (for example, 100 × 100) photosensitive portions 11 arranged in a matrix, and is formed on, for example, a single semiconductor substrate. Each column in the vertical direction in the photosensitive portion 11 shares the semiconductor layer 21 that is integrally continuous, and the semiconductor layer 21 is used as a transfer path for charges in the vertical direction (electrons are used in this embodiment). It is possible to employ a configuration in which a semiconductor substrate is provided with a horizontal transfer portion Th that is a CCD that receives charges from one end of the semiconductor layer 21 and transfers the charges in the horizontal direction.

  That is, as shown in FIG. 4, the semiconductor layer 21 serves as the photosensitive portion 11 and the charge transfer path, and is similar to a frame transfer (FT) type CCD image sensor. Similarly to the FT type CCD image sensor, a light-shielded accumulation region Db is provided adjacent to the imaging region Da in which the photosensitive portions 11 are arranged, and charges accumulated in the accumulation region Db are transferred to the horizontal transfer unit Th. To do. The transfer of charges from the imaging area Da to the storage area Db is performed at once in the vertical blanking period, and the horizontal transfer unit Th transfers charges for one horizontal line in one horizontal period. The charge extraction unit 14 illustrated in FIG. 1 represents a function including a horizontal transfer unit Th along with a function as a charge transfer path in the vertical direction in the semiconductor layer 21. However, the charge accumulation unit 13 does not mean the accumulation region Db, but represents a function of accumulating charges in the imaging region Da. In other words, the accumulation region Db is included in the charge extraction unit 14.

  The semiconductor layer 21 is doped with impurities, the main surface of the semiconductor layer 21 is covered with an insulating film 22 made of an oxide film, and a plurality of control electrodes 23 are arranged on the semiconductor layer 21 via the insulating film 22. . This light detection element 1 has a structure known as a MIS element, but a normal MIS element is that a plurality of (five in the illustrated example) control electrodes 23 are provided in a region functioning as one light detection element 1. Is different. A material is selected for the insulating film 22 and the control electrode 23 so that light having the same wavelength as the light emitted from the light source 2 to the target space can be transmitted. When light enters the semiconductor layer 21 through the insulating film 22, the semiconductor layer 21. A charge is generated inside the. The conductivity type of the semiconductor layer 21 in the illustrated example is n-type, and electrons e are used as charges generated by light irradiation. FIG. 3 shows only a region corresponding to one photosensitive portion 11, and a plurality of regions having the structure shown in FIG. 3 are arranged on the semiconductor substrate (not shown) and the charge extraction is performed. A structure to be part 14 is provided. The vertical transfer unit provided as the charge extraction unit 14 is assumed to transfer charges in the left-right direction in FIG. 3, but it is also possible to adopt a configuration in which charges are transferred in a direction orthogonal to the plane in FIG. is there. In addition, when transferring charges in the horizontal direction in the figure, it is desirable to set the width dimension of the control electrode 23 in the horizontal direction to about 1 μm.

  In the light detection element 1 having this structure, when a positive control voltage + V is applied to the control electrode 23, a potential well (depletion layer) 24 that accumulates electrons e in a portion corresponding to the control electrode 23 is formed in the semiconductor layer 21. The That is, when light is applied to the semiconductor layer 21 with a control voltage applied to the control electrode 23 so as to form the potential well 24 in the semiconductor layer 21, a part of the electrons e generated in the vicinity of the potential well 24. Are captured in the potential well 24 and accumulated in the potential well 24, and the remaining electrons e disappear due to recombination in the deep part of the semiconductor layer 21. Further, the electrons e generated at a location away from the potential well 24 are also extinguished by recombination in the deep part of the semiconductor layer 21.

  Since the potential well 24 is formed at a portion corresponding to the control electrode 23 to which the control voltage is applied, the potential well 24 along the main surface of the semiconductor layer 21 is changed by changing the number of the control electrodes 23 to which the control voltage is applied. (In other words, the area of a region that generates a charge that can be used on the light receiving surface) can be changed. That is, changing the number of control electrodes 23 to which the control voltage is applied means adjusting sensitivity in the sensitivity control unit 12. For example, when the control voltage + V is applied to three control electrodes 23 as shown in FIG. 3A and when the control voltage + V is applied to one control electrode 23 as shown in FIG. Since the area occupied by the potential well 24 on the light receiving surface changes, and the area of the potential well 24 is larger in the state of FIG. 3A, the same light quantity is obtained compared to the state of FIG. As a result, the ratio of the charge that can be used increases and the sensitivity of the photosensitive portion 11 is substantially increased. Thus, it can be said that the photosensitive portion 11 and the sensitivity control portion 12 are constituted by the semiconductor layer 21, the insulating film 22, and the control electrode 23. The potential well 24 functions as the charge accumulation unit 13 because it holds charges generated by light irradiation.

  In order to extract charges from the potential well 24, a technique similar to that of the FT type CCD may be employed. After the electrons e are accumulated in the potential well 24, a control voltage of an applied pattern different from that during charge accumulation is controlled. By applying the voltage to the electrode 23, the electrons e accumulated in the potential well 24 can be transferred in one direction (for example, the right direction in the figure). That is, the semiconductor layer 21 can be used as a charge transfer path in the same manner as the vertical transfer portion of the CCD. Further, the electric charge is transferred through the horizontal transfer portion Th shown in FIG. 4 and is taken out of the photodetecting element 1 from an electrode (not shown) provided on the semiconductor substrate. In short, by controlling the application pattern of the control voltage to the control electrode 23, the sensitivity of each photosensitive portion 11 is controlled, charges generated by light irradiation are integrated, and the integrated charges are transferred. Can do.

  The sensitivity control unit 12 in the present embodiment switches the sensitivity of the photosensitive unit 11 to two levels of high and low by switching the area for generating available charges into two levels of large and small, and the received light amount A0, A1, A2, A3. High sensitivity is set only during the light receiving period in which the charge corresponding to any one is to be generated by the photosensitive portion 11 (the area for generating the charge is increased), and low sensitivity is set during the other holding period. The light receiving period for high sensitivity and the holding period for low sensitivity are set in synchronization with the modulation signal for driving the light source 2. In addition, after the charges are accumulated in the potential well 24 over a plurality of periods of the modulation signal, the charges are extracted to the outside of the light detection element 1 through the charge extraction unit 14. Charges are accumulated over a plurality of periods of the modulation signal because the period during which the photosensitive unit 11 generates usable charges within one period of the modulation signal is short (for example, if the frequency of the modulation signal is 20 MHz). This is because less than a quarter of 50 ns is generated. By integrating charges for a plurality of periods of the modulation signal, signal charges (charges corresponding to light emitted from the light emission source 2) and noise charges (external light components and shot noise generated inside the light detection element 1) And a large SN ratio can be obtained.

  By the way, in this embodiment, the structure which produces | generates two types of electric charges corresponding to received light quantity A0, A1, A2, A3 within one period of a modulation signal by using the two photosensitive parts 11 is employ | adopted. . That is, an arithmetic unit is constituted by two photosensitive units 11 adjacent in the vertical direction, and an electrical output obtained from the two photosensitive units 11 serving as an arithmetic unit is used to obtain a pixel value for one pixel of a distance image. A period for generating charges corresponding to the received light amounts A0 and A2 and a period for generating charges corresponding to the received light amounts A1 and A3 are provided by the two photosensitive units 11 serving as calculation units. Further, regarding the period for generating charges corresponding to the received light amounts A0 and A2, the period in which one of the two photosensitive units 11 serving as the calculation unit generates charges corresponding to the received light amount A0 and the other corresponds to the received light amount A0. The charge generation period is divided into two periods, ie, a period for generating the charge to be generated. For the period for generating the charge corresponding to the received light quantity A1 and A3, one of the two photosensitive units 11 serving as the calculation unit has the charge corresponding to the received light quantity A1. The generation period and the other period are divided into two periods, a period for generating charges corresponding to the received light quantity A1. In short, all the photosensitive portions 11 generate charges corresponding to the received light amounts A0, A1, A2, and A3 in four periods, respectively.

  The operation will be specifically described below. In the example shown in FIG. 3, an example in which five control electrodes 23 are provided for one photosensitive portion 11 is shown. However, two control electrodes 23 on both sides are charged (electrons e) by the photosensitive portion 11. In the case where two photosensitive units 11 are used as an arithmetic unit, the adjacent photosensitive units are formed. Since any one of the photosensitive portions 11 forms a barrier between the 11 potential wells 24, it is sufficient to provide three photosensitive electrodes 11 for each of the photosensitive portions 11. With this configuration, the occupation area per one photosensitive portion 11 is reduced, and it is possible to suppress a decrease in resolution in the line-of-sight direction while using the two photosensitive portions 11 as a calculation unit.

  Here, as shown in FIG. 5, the numbers (1) to (6) are assigned to each control electrode 23 in order to distinguish the three control electrodes 23 respectively provided in the two photosensitive portions 11 as the calculation unit. Is attached. The two photosensitive portions 11 having the control electrodes 23 assigned with the numbers (1) to (6) correspond to one pixel in the distance image sensor. In addition, it is desirable to provide an overflow drain in association with the photosensitive portion 11 for each pixel.

  5A and 5B show a state in which a control voltage + V is applied to the control electrode 23 with a different application pattern from the control circuit unit 3 (between a substrate electrode (not shown) provided on the semiconductor substrate and the control electrode 23). As can be seen from the shape of the potential well 24, in FIG. 5A, the control electrodes (1) to (3) out of the two photosensitive portions 11 serving as one pixel are shown. And a positive control voltage + V is applied to the central control electrode (5) among the remaining control electrodes (4) to (6). In FIG. 5B, a positive control voltage + V is applied to the central control electrode (2) among the control electrodes (1) to (3), and the remaining control electrodes (4) to (6) are applied. A positive control voltage + V is applied. In other words, the application pattern of the control voltage + V applied to the two photosensitive portions 11 constituting one pixel is alternately replaced. The timing of switching the application pattern of the control voltage + V applied to the two photosensitive portions 11 is the timing of the opposite phase (the phase is 180 degrees different) in the modulation signal. In addition, except for the period in which the control voltage + V is simultaneously applied to the three control electrodes 23 provided in each photosensitive portion 11, one central control electrode 23 (that is, the control electrode) provided in each photosensitive portion 11 is provided. (2) The control voltage + V is applied only to (5)), and the other control electrodes 23 are kept at 0V.

  For example, when the charges corresponding to the received light amounts A0 and A2 are alternately generated in the two photosensitive portions 11 constituting one pixel, the charges corresponding to the received light amount A0 in one photosensitive portion 11 as shown in FIG. In the light receiving period Tw in which the control voltage + V is applied to the three control electrodes (1) to (3) in order to generate the voltage, the other photosensitive portion 11 has 1 to hold the charge corresponding to the received light quantity A2. A control voltage + V is applied only to the control electrodes (5). Similarly, in the light receiving period Tw in which the control voltage + V is applied to the three control electrodes (4) to (6) in order to generate a charge corresponding to the received light quantity A2 in one photosensitive portion 11, the other The photosensitive portion 11 applies a control voltage + V only to one control electrode (2) in order to hold a charge corresponding to the received light quantity A0. Further, the control voltage + V is applied only to the control electrodes (2) and (5) in the holding period other than the light receiving period Tw for generating charges corresponding to the received light amounts A0 and A2. FIGS. 2B and 2C show the application timing of the control voltage + V to the control electrodes (1) to (6) when accumulating charges corresponding to the received light amounts A0 and A2. In the figure, the hatched portion indicates a state where the control voltage + V is applied, and the blank portion indicates a state where no voltage is applied to the control electrodes (1) to (6).

  The same applies to the case where the charges corresponding to the received light amounts A1 and A3 are generated in the two photosensitive portions 11 constituting one pixel, and the case where the charges corresponding to the received light amounts A0 and A2 are generated is different from the control electrode 23. The only difference is that the timing at which the control voltage + V is applied differs by 90 degrees in the phase of the modulation signal.

  The period for generating the charges corresponding to the received light amounts A0 and A2 and the period for generating the charges corresponding to the received light amounts A1 and A3 are both fixed periods of one period or more (preferably for a plurality of periods) of the modulation signal. With this period as a detection period, charges for a plurality of periods of the modulation signal are accumulated in the charge accumulation unit 13. In addition, the charge is transferred from the imaging region Da to the storage region Db with the period from the next detection period as the readout period for each detection period.

  In the present embodiment, charges corresponding to the received light amount A0 are accumulated in the potential well 24 corresponding to the control electrodes (1) to (3), and charges corresponding to the received light amount A2 are stored in the control electrodes (4) to (6). The detection period for accumulating in the corresponding potential well 24 is continuously provided a plurality of times, and the charge corresponding to the received light amount A1 is accumulated in the potential well 24 corresponding to the control electrodes (1) to (3) and corresponds to the received light amount A3. The operation of continuously providing a plurality of detection periods for accumulating the charge to be stored in the potential well 24 corresponding to the control electrodes (4) to (6) is repeated. That is, as shown in FIG. 7, the integration period Pa in which the detection periods S11, S12,... And the readout periods R11, R12,. The detection periods S21, S22,... For accumulating charges corresponding to A1 and A3 and the integration period Pb in which the readout periods R21, R22,... Are repeated a plurality of times are alternately repeated, and each of the integration periods Pa and Pb is repeated. Charges corresponding to the received light amounts A0, A1, A2, A3 are integrated. Since calculation for obtaining the phase difference ψ (or distance) requires charges corresponding to the light receiving periods Tw synchronized with the four phases of the modulation signal, in this embodiment, integration is performed in two integration periods Pa and Pb, respectively. The phase difference ψ (or distance) is calculated using the charge amount of the obtained charges. In each detection period S11, S12,..., S21, S22,..., The control circuit unit determines which received light quantity A0, A1, A2, A3 corresponds to the charge integration unit 13 (potential well 24). 3 is selected by controlling the sensitivity of the sensitivity control unit 13 (controlling the control voltage applied to the control electrode 23). Note that the distance may be calculated using an average value instead of the integrated value of the charge amount integrated in the integration periods Pa and Pb.

  In the readout periods R11, R12,..., R21, R22,..., Charges corresponding to the received light amounts A0, A1, A2, A3 of the light receiving period Tw synchronized with the four phases of the modulation signal are supplied to the light output element 1. Take out to the outside as electrical output. The extracted electrical output is used for the calculation of the phase difference ψ in the image generation unit 4, and as a result, the distance to the object Ob existing in the line-of-sight direction corresponding to each pixel can be obtained.

  In the above example, the control voltage applied simultaneously to the three control electrodes 23 ((1) to (3) or (4) to (6)) and one control electrode 23 ((2) or (5)) Since the control voltage applied only to is equal, the area of the potential well 24 changes, but the depth of the potential well 24 is equal. In this case, the charges generated at the control electrode 23 ((1) (3) or (4) (6)) to which no control voltage is applied flow into the potential well 24 with a similar probability. That is, by applying the control voltage + V to only one of the three control electrodes 23 constituting the photosensitive portion 11, the region functioning as the charge accumulation portion 13 and all the three control electrodes 23 are applied. A similar amount of charge flows into both the region to which the control voltage + V is applied. That is, since the noise component flowing into the potential well 24 holding the charge is relatively large, the dynamic range is lowered.

  Therefore, as shown in FIG. 6, the control voltage applied simultaneously to each of the three control electrodes (1) to (3) or (4) to (6) provided in the two photosensitive portions 11 serving as the calculation unit is It is desirable to set the potential well 24 to be higher than the control voltage applied to only one control electrode (2) or (5), and to set the large-area potential well 24 deeper than the small-area potential well 24. As described above, the potential well 24 that mainly generates charges (electrons e) is made deeper than the potential well 24 that mainly holds charges, so that the control electrode (1) to which no control voltage is applied is applied. Charges generated at the sites corresponding to (3) or (4) and (6) are likely to flow into the deeper potential well 24. That is, as compared with the case where a constant control voltage + V is applied to the control electrode 23, the noise component flowing into the potential well 24 holding the charge can be reduced.

  In the above-described example, the photosensitive unit 11 that generates charges corresponding to the four types of received light amounts A0, A1, A2, and A3 is determined in each integration period Pa and Pb. There may be errors due to position differences. In particular, if there is a step in the object Ob and the photosensitive portion 11 corresponding to the received light amount A0 and the received light amount A2 coincides with the part straddling the step, the reliability of the required distance is lowered. .

  In order to solve this type of problem, the charge corresponding to the received light amount A0 is accumulated in the potential well 24 corresponding to the control electrodes (1) to (3) and the charge corresponding to the received light amount A2 is detected for each detection period. The state of accumulation in the potential well 24 corresponding to the control electrodes (4) to (6) and the charge corresponding to the received light amount A2 are accumulated in the potential well 24 corresponding to the control electrodes (1) to (3) and the received light amount. A state in which charges corresponding to A0 are accumulated in the potential well 24 corresponding to the control electrodes (4) to (6), and a charge corresponding to the received light amount A1 is potential well 24 corresponding to the control electrodes (1) to (3). In the potential well 24 corresponding to the control electrodes (4) to (6) and the charge corresponding to the received light amount A3. Circulates four states including the state in which the potential well 24 corresponding to (1) to (3) is accumulated and the charge corresponding to the received light quantity A1 is accumulated in the potential well 24 corresponding to the control electrodes (4) to (6). Can be switched. That is, for each detection period, the charges accumulated in each charge accumulation unit 13 are cyclically selected from the charges corresponding to the respective received light amounts A0, A1, A2, A3. By repeating this operation, the charges corresponding to the received light amounts A0, A1, A2, and A3 in the four types of light receiving periods Tw can be taken out as an electrical output to the outside of the light output element 1 by the reading operation of an integral multiple of four times. it can.

  More specifically, as shown in FIG. 8A, the image generation unit 4 uses two different modulation signals in the readout periods R1, R2, R3, and R4 provided for each of the detection periods S1, S2, S3, and S4. An electrical output corresponding to the light receiving period Tw synchronized with the phase is given from the light detection element 1. Since the calculation for obtaining the phase difference ψ (or distance) requires an electrical output corresponding to the light receiving period Tw of all phases, the electric output corresponding to the four detection periods S1, S2, S3, and S4 is used. The phase difference ψ (or distance) is calculated. In the illustrated example, since the distance to the object Ob is obtained in the period P1 of the four detection periods S1, S2, S3, S4 and the readout periods R1, R2, R3, R4, the period P1 corresponds to one frame of the image. It corresponds to time.

  In the above-described period P1, as shown in FIG. 8B, two detection periods S1 and S2 in which electrical outputs corresponding to the received light amounts A0 and A2 are obtained, and electrical outputs corresponding to the received light amounts A1 and A3. Are included in two detection periods S3 and S4, and in the two detection periods S1 and S2 in which electrical outputs corresponding to the received light amounts A0 and A2 are obtained, the received light amounts A0 and A2 are obtained. In addition, the photosensitive portion 11 having the respective received light amounts A1 and A3 is replaced in two detection periods S3 and S4 in which electrical outputs corresponding to the received light amounts A1 and A3 are obtained. Therefore, the integrated value (or average value) of the electrical outputs obtained in the two detection periods S1 and S2 in which the electrical outputs corresponding to the received light amounts A0 and A2 are obtained is obtained for each received light amount A0 and A2. The integrated value (or average value) of the electrical outputs obtained in the two detection periods S3 and S4 in which the electrical outputs corresponding to the light amounts A1 and A3 are obtained is obtained for each received light amount A1 and A3, and four integrated values are obtained. (Or average value) is used as values corresponding to the received light amounts A0, A1, A2, and A3, respectively, and the calculation of equation (1) is performed. By such calculation, it is possible to reduce a decrease in reliability of distance measurement due to a shift in the position of the photosensitive portion 11 when obtaining an electric output corresponding to each of the received light amounts A0, A1, A2, and A3.

  In the configuration example of the distance image sensor described above, the four light receiving periods Tw corresponding to the received light amounts A0, A1, A2, and A3 are set so that the phase interval is 90 degrees in one cycle of the modulation signal. However, if the phase with respect to the modulation signal is known, the four light receiving periods Tw can be set at appropriate intervals other than 90 degrees. However, the formula for obtaining the phase difference ψ differs if the interval is different. In addition, the period for taking out the electric charges (electrical output) corresponding to the received light amounts in the four light receiving periods Tw is within a time period in which the reflectance and the external light component of the object Ob do not change and the phase difference ψ does not change. It is not essential to extract four types of electrical outputs within one period of the modulation signal. Furthermore, when there is an influence of disturbance light such as sunlight or illumination light, it is desirable to dispose an optical filter that transmits only the wavelength of light emitted from the light source 2 in front of the photosensitive portion 11. In the configuration example described with reference to FIGS. 5 and 6, three control electrodes 23 are associated with each photosensitive portion 11, but four or more control electrodes 23 may be provided. In the above example, the same configuration as the FT type CCD image sensor is adopted, but the same configuration as the interline transfer (IT) method and the frame interline transfer (FIT) method is adopted. Is also possible.

  In the configuration example described above, in the detection period in which each of the two photosensitive units 11 arranged in the vertical direction in the light detection element 1 is used as a calculation unit, and the electrical output of the photosensitive unit 11 is read once from the light detection element 1, the calculation is performed. The light receiving period Tw of each photosensitive unit 11 is controlled in the control circuit unit 3 so that the two photosensitive units 11 serving as a unit can obtain electric outputs corresponding to the received light amounts A0 and A2 or the received light amounts A1 and A3. In other words, the electrical outputs of two light receiving periods Tw out of the four light receiving periods Tw set in synchronization with the prescribed phase in the modulation signal are collectively read out. In contrast to this configuration, each of the four photosensitive sections 11 arranged in the vertical direction is used as a calculation unit, and each of the photosensitive units whose electric outputs in four light receiving periods Tw set in synchronization with the phase of the modulation signal are used as a calculation unit. It is also possible to control the light receiving period Tw of the photosensitive portion 11 as obtained by the portion 11. In this case, the electric outputs of the four light receiving periods Tw corresponding to the received light amounts A0, A1, A2, A3 can be read out in one detection period.

In the configuration example described above, the integrated value or average value of the electrical outputs corresponding to the received light amounts A0, A1, A2, and A3 obtained from the light detection element 1 is obtained, and this value is used as the pixel value of each pixel. Although the distance is obtained, the image generation unit 4 receives the electrical output of each photosensitive unit 11 for each detection period, and if the electrical output is not averaged, it is necessary to obtain the distance in each one photosensitive unit 11. Since four types of electrical outputs corresponding to the received light amounts A0, A1, A2, and A3 are obtained, the distance to the object Ob can be obtained using these four types of electrical outputs. Further, the amount of change in the amount of received light received by the light detection element 1 is smaller than the amplitude of the intensity modulation of the light emitted from the light source 2 to the target space if the disturbance light does not change with time. Therefore, the distance is obtained as described above by combining the electrical outputs of the photosensitive unit 11 which is a calculation unit at all times, and the received light amounts A0, A1, A2, A3 received by the photosensitive unit 11 which is the calculation unit in order to obtain the distance. Is determined to be an abnormal value when the change width (the difference between the maximum value and the minimum value) is larger than the expected change width, and if it is an abnormal value, only an electric signal obtained from one photosensitive portion 11 is used. It is also possible to obtain the distance.

It is a block diagram which shows embodiment of this invention. It is operation | movement explanatory drawing same as the above. It is operation | movement explanatory drawing of the principal part of the photon detection element used for the same as the above. It is a top view of the photon detection element used for the same as the above. It is operation | movement explanatory drawing of the principal part of the photon detection element used for the same as the above. It is operation | movement explanatory drawing of the principal part of the photon detection element used for the same as the above. It is operation | movement explanatory drawing same as the above. It is operation | movement explanatory drawing of the other operation example same as the above.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photodetector 2 Light emission source 3 Control circuit part 4 Image generation part 5 Light reception optical system 11 Photosensitive part Ob Object

Claims (2)

A target space having a light emitting source that irradiates the target space with light whose intensity is modulated with a modulation signal of a predetermined period, and a plurality of photosensitive units that receive light from the target space and generate charges corresponding to the amount of received light, respectively. A light detection element that captures the light, a control circuit unit that controls a light receiving period in which each photosensitive unit receives light from the target space, and a distance to the target using the charge generated by the photosensitive unit. An image generation unit that generates a distance image as a pixel value, the light receiving period is set to be shorter than the period of the modulation signal in synchronization with the phase of the modulation signal, and the light detection element includes a plurality of adjacent photosensitive units. The calculation unit is a charge obtained by accumulating charges obtained in a plurality of light receiving periods for each detection period which is a period of one or more periods of the modulation signal , and the light receiving period of each photosensitive unit serving as a calculation unit is given as Different of the phases for each detection period Transfer timing of the charge so as to change the light receiving period for the phase are controlled by the control circuit unit, the image generating unit obtains a distance using the amount of charge accumulated by the light receiving period the amount of charge of a plurality of detection periods, the distance distance image sensor, characterized in that the pixel values of the distance image. Before Symbol image generation unit, in a plurality of detection periods for accumulating charges obtained by the respective photosensitive portions serving as operation unit, wherein, characterized in that the in equal number to the number of the light receiving period for each detection period Item 1. The distance image sensor according to item 1.

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