JP4715216B2 - Ranging device - Google Patents

Description

  The present invention projects intensity-modulated light into a target space and receives light from the target space, and obtains a phase difference between the projected intensity-modulated light and the received light to obtain an object existing in the target space. The present invention relates to a distance measuring device for obtaining a distance.

  Conventionally, light modulated by using a modulation signal having an appropriate waveform (intensity modulated light) is projected from the light source to the target space, and the light received from the target space has a light reception output having a magnitude corresponding to the amount of received light. The phase difference between the intensity modulated light projecting and receiving is obtained from the relationship between the modulation signal that modulates the light source and the light receiving output of the light detecting element, and the phase difference is converted into a distance. A distance measuring device has been proposed (see, for example, Patent Document 1).

  For example, a sine wave is used as the waveform of the modulation signal, and four detection values obtained by sampling the received light output at timings that are 90 degrees different from each other in the modulation signal are included in the detection value group. The tangent of the phase difference between light projection and light reception can be obtained from the detected value.

For example, if the modulation signal is a sine wave as shown in FIG. 15A and the intensity of light incident on the light detection element changes as shown in FIG. 15B, the modulation signal S and the light detection are detected. The intensity I of light incident on the element can be expressed as follows, for example.
S = α · sinωt
I = A · sin (ωt + δ) + B
Where α is the amplitude of the modulation signal, A is the amplitude of the light incident on the light detection element, B is the average value of the maximum and minimum values of the light incident on the light detection element, and the amplitude depends on the intensity of the ambient light It becomes the value which added. Further, ω is an angular frequency, δ is an initial phase, and when the phase difference between light projection and light reception is θ, δ = −θ. Assuming that the sampling period of the received light output is a period of 180 degrees, there is no change in the phase difference θ during the sampling period, and there is no change in the light attenuation rate from the light projection to the light reception, and FIGS. ), The detection value corresponding to the received light amount obtained in the period of 0 to 180 degrees in the modulation signal is A0, the detection value of 90 to 270 degrees is A1, the detection value of 180 to 360 degrees is A2, and 270 to 90. If the detected value of (450) degrees is A3, the following equation is obtained. Each detection value A0 to A3 corresponds to a received light amount obtained by integrating the intensity of the received light in each period of the modulation signal.
A0 = A ′ · cos θ + B ′
A1 = A ′ · sin θ + B ′
A2 = −A ′ · cos θ + B ′
A3 = −A ′ · sin θ + B ′
However, A ′ and B ′ are constants. Therefore, the phase difference θ can be expressed by the following equation using the detected values A0, A1, A2, and A3.
tan θ = (A3-A1) / (A2-A0)
Since the phase difference θ [rad] corresponds to the round-trip time of light to the object, the distance L [m] is expressed by the following equation using the light beam c [m / s] and the frequency f [Hz] of the modulation signal. Can be represented.
L = (c / f) · (θ / 4π)
That is, when the phase difference θ is obtained, the distance L to the object can be obtained. In other words, to obtain the distance L using the above equation, an operation for obtaining the phase difference θ from the detected values A0, A1, A2, and A3 is required.
JP 2004-356594 A

By the way, in order to obtain the phase difference θ from the detection values A0, A1, A2, and A3, the following equation is required.
θ = tan ⁻¹ S
However, S = (A3-A1) / (A2-A0).
When tan ⁻¹ x is expressed as a power series by Taylor expansion, the following equation is obtained.
^{tan -1 x = x- (x 3} /3) + (x 5/5) - (x 7/7) + (x 9/9) - ...
It is required to calculate the above expression up to the term that can ensure the required accuracy. For example, if up to 5 items are calculated, x 3rd power, 5th power, 7th power, and 9th power are required. Since division by a non-exponential value is also required, the calculation load becomes very large. Furthermore, since exponent calculation is required, floating point arithmetic is required to ensure accuracy. That is, the processing load increases.

  On the other hand, a data table in which the value of tan θ and the phase difference θ are associated in advance is prepared, and the phase difference θ is obtained by comparing tan θ obtained from the detected values A0, A1, A2, and A3 with the data table. However, a large-capacity storage unit is required to create the data table.

  The present invention has been made in view of the above-mentioned reasons, and the purpose thereof is to perform an approximate operation using an interval function, so that it is not necessary to provide a storage unit such as a data table, and the calculation load is reduced. An object of the present invention is to provide a distance measuring device which can be reduced, and can easily and rapidly perform a calculation process for obtaining a distance.

  According to the first aspect of the present invention, there is provided a light emitting source that projects intensity-modulated light whose intensity is modulated onto a target space, a light detecting element that receives light from the target space and obtains a light-receiving output corresponding to the amount of received light. A sampling unit that extracts a detection value group consisting of a plurality of detection values by sampling the light reception output of the light detection element at a prescribed timing, and a light emission source that emits light by substituting the detection value group into a predetermined function An arithmetic processing unit for obtaining a value corresponding to the phase difference between the intensity-modulated light and the intensity-modulated light received by the light detection element, and the arithmetic processing unit sets a section in which one cycle of the intensity-modulated light is divided into a plurality of In addition, a section discriminating section that discriminates a section in which a phase difference exists based on a relationship between a plurality of detected values that are detection value groups, and a section discriminating section that approximates the function by a plurality of section functions set for each section. Corresponding to the section By substituting the detected value group between functions, characterized in that it comprises a calculation unit for obtaining a one-to-one corresponding function values to the phase difference.

  According to this configuration, one period of the intensity-modulated light is divided into a plurality of sections, the section where the phase difference exists is determined from the detected value group, and the target value is obtained by substituting the detected value group. Since the function to be obtained is approximated by using an interval function set for each interval, if the information indicated by the detection value group is extracted by a single function, complicated calculation is required or a large value is handled in the calculation process Even if this is necessary, the load of the arithmetic processing can be reduced by performing the approximate calculation using a relatively simple interval function. In addition, since it is not necessary to use a data table for associating the detected value group with the phase difference, a storage area for the data table is not required, and no interpolation calculation is required.

  According to a second aspect of the present invention, in the first aspect of the present invention, the light source is a sinusoidal waveform of the intensity modulated light, the function is a function that is linear with respect to the phase difference, and the arithmetic processing unit is the detected value. As a group, three or more detection values having different phases in intensity-modulated light at equal intervals are used, and the calculation unit sets an interval function using at least one of a tangent and a cotangent of a value corresponding to the phase difference. And at least one of the tangent and the cotangent obtained by dividing one of the two differences obtained from each of the two detected values having different phases in the detected value group by the other is an interval function. The function value of the function is obtained by substituting for.

  According to a third aspect of the present invention, in the first aspect of the present invention, the light source is a sine wave as the waveform of the intensity modulated light, the function is a function that is linear with respect to a phase difference, and the arithmetic processing unit is the detection value group. As described above, four detected values having different phases in intensity-modulated light at intervals of 90 degrees are used, and the calculation unit sets an interval function using at least one of a tangent and a cotangent of a value corresponding to the phase difference. In the detected value group, at least one of the tangent and the cotangent obtained by dividing one of two differences obtained from two detected values each having a phase difference of 180 degrees by the other is defined as an interval function. The function value of the function is obtained by substituting.

  According to a fourth aspect of the present invention, in the first aspect of the present invention, the light source is a sinusoidal waveform of the intensity-modulated light, the function is a linear function with respect to a phase difference, and the arithmetic processing unit is the detected value group. As described above, three detection values whose phases in the intensity-modulated light are different at intervals of 90 degrees are used, and the calculation unit sets an interval function using at least one of a tangent and a cotangent of a value corresponding to the phase difference. In the detected value group, at least one of the tangent and the cotangent obtained by dividing one of two differences obtained from two detected values each having a phase difference of 90 degrees by the other is defined as an interval function. The function value of the function is obtained by substituting.

  According to the configuration of the invention of any one of claims 2 to 4, since all of the detection values are three or more detection values whose phases in the intensity modulated light are different at equal intervals, the subtraction and division of the detection values are performed. The value corresponding to the tangent and cotangent of the value corresponding to the phase difference can be obtained, and the interval function is set using at least one of the tangent and the cotangent, so the phase difference can be obtained by simple calculation. Can do. In addition, since a linear function is approximated by an interval function, there is almost no change in accuracy or reliability due to the magnitude of the phase difference. Note that the value corresponding to the phase difference may indicate the phase difference itself, or may indicate a value obtained by shifting the phase difference by a certain phase.

  According to a fifth aspect of the present invention, in the second to fourth aspects of the present invention, the section discriminating unit includes two difference codes obtained from two detection values each having a different phase in the detection value group. Using the magnitude of the absolute value of each difference, a section in which the phase difference exists is determined in units of 45 degrees, and the arithmetic unit calculates 8 from 0 degrees to 360 degrees with respect to a value θ corresponding to the phase difference. Each interval function in the interval is set as tanθ, 2-cotθ, 2-cotθ, 4 + tanθ, 4 + tanθ, 6-cotθ, 6-cotθ, and 8 + tanθ, respectively.

  According to this configuration, a value corresponding to the phase difference can be obtained by simple calculation of subtraction and division of the detection value. In addition, a substantially linear function can be approximated using a simple interval function.

According to a sixth aspect of the present invention, in the second to fourth aspects of the invention, the section discriminating unit includes two difference codes obtained from two detection values each having a different phase in the detection value group. Using the magnitude of the absolute value of each difference, a section in which the phase difference exists is determined in units of 45 degrees, and the calculation unit calculates t ⁺ = (1 + tan θ) / (with respect to the value θ corresponding to the phase difference. 1−tan θ), t ⁻ = (1−tan θ) / (1 + tan θ), each interval function in 8 intervals from 0 degrees to 360 degrees is expressed as (1 + tan θ−t ⁻ ) / 2, (3-cot θ, respectively). −t ⁻ ) / 2, (5-cot θ + t ⁺ ) / 2, (7 + tan θ + t ⁺ ) / 2, (9 + tan θ−t ⁻ ) / 2, (11−cot θ−t ⁻ ) / 2, (13−cot θ + t ⁺ ) / 2, (15 + tanθ + t ⁺ ) / 2 It is characterized by being.

  According to this configuration, a value corresponding to the phase difference can be obtained by simple calculation of subtraction and division of the detection value. In addition, a substantially linear function can be approximated using a simple interval function that can be expressed by four arithmetic operations. In particular, since the approximation closer to a straight line is possible than the interval function used in claim 5, it is possible to obtain a more reliable value.

  According to the configuration of the present invention, one period of the intensity-modulated light is divided into a plurality of sections, the section where the phase difference exists is determined from the detected value group, and the detected value group is further substituted for the purpose. Since the function for obtaining the value is approximated by using an interval function set for each interval, if the information indicated by the detection value group is extracted by a single function, complicated calculation is required or a large value in the calculation process Even when it is necessary to handle the above, there is an advantage that the load of the arithmetic processing can be reduced by performing the approximate calculation using a relatively simple interval function. Further, since it is not necessary to use a data table for associating the detected value group with the phase difference, a storage area for the data table is not required, and an interpolation calculation is not required.

(Embodiment 1)
In the present embodiment, as shown in FIG. 1, a case where only one photodetecting element 2 is provided will be described. However, a plurality of (for example, 100 × 100) photodetecting elements 2 are arranged on lattice points of a planar lattice. Even in the case of arranging the image sensors by arranging them, the same technique as that of the embodiment described below can be adopted.

  As shown in FIG. 1, the distance measuring apparatus according to the present embodiment includes a light source 1 that projects light into a target space, and projects light projected from the light source 1 into the target space and reflected by an object 3 in the target space. A light detecting element 2 for receiving light is provided. As the light emitting source 1, for example, a plurality of light emitting diodes arranged on a plane is used. Alternatively, a combination of a semiconductor laser and a diverging lens may be used for the light source 1. The light source 1 modulates the amount of light output by the modulation signal output from the timing control circuit 4. That is, the intensity-modulated light modulated by the modulation signal is projected from the light source 1 into the target space. A sine wave is used as the modulation signal, and the frequency of the modulation signal is, for example, 20 MHz.

  The light detection element 2 outputs a light reception output corresponding to the amount of light received. The light reception output corresponding to the amount of received light means that the light reception output corresponds to the product of the light reception intensity and the light reception time. When the light detection element 2 has a structure that does not have a charge accumulation function like a photodiode or a phototransistor, a light reception output corresponding to the instantaneous value of the light reception intensity is output, and also like a CCD image sensor. In the case of a structure having a charge accumulation function, a light reception output corresponding to the amount of charge accumulated according to the light reception time can be obtained.

  The output of the light detection element 2 is input to the sampling unit 5, and the light reception output of the light detection element 2 is sampled at a timing that matches the phase of the modulation signal. In the sampling unit 5, for example, four samples whose phases are different by 90 degrees, such as 0 to φ degrees, 90 to (90 + φ) degrees, 180 to (180 + φ) degrees, and 270 to (270 + φ) degrees in the phase of the modulation signal. The received light output is sampled for each period Ps, and the integrated value of the sampling period Ps (see FIG. 15) is output as the detected value. φ can be set appropriately, for example, set to 180 degrees. Since the four detection values obtained in the sampling period Ps synchronized with four phases having different modulation signals are a set of data for obtaining the phase difference θ, these detection values are referred to as a detection value group. To do. In addition, the detected values obtained in each of the sampling periods Ps that are synchronized with the phase of the modulation signal are A0, A1, A2, and A3, respectively.

The detected value group is input to the arithmetic processing unit 6 configured by a computer. The arithmetic processing unit 6 of the present embodiment obtains a value corresponding to the phase difference from when the intensity-modulated light is projected onto the target space by the light source 1 to when it is received by the light detection element 2 according to the principle described below. As described in the related art, the four detection values A0, A1, A2, and A3 constituting the detection value group and the phase difference θ ideally have a relationship of the following equation.
tan θ = (A3-A1) / (A2-A0)
By the way, in the range where the phase difference θ is 0 to 45 degrees, the value range of tan θ is 0 to 1, and the value changes substantially linearly with respect to the change of the phase difference. On the other hand, in the range where the phase difference θ is 45 to 90 degrees, the value range of tan θ is 1 to infinity, but the value range of cot θ is 1 to 0 and changes almost linearly with respect to the change of the phase difference. Therefore, when 2-cot θ is used so that the range of the phase difference θ is 45 to 90 degrees, the value changes almost linearly in the range of the phase difference θ of 45 to 90 degrees. . That is, if the function is approximated using tan θ in the section where the phase difference θ is 0 to 45 degrees and 2-cot θ in the section where the phase difference θ is 45 to 90 degrees, the value is almost equal in the section of 0 to 90 degrees. It becomes possible to change linearly. The same applies to the case where the phase difference θ is another value. The range in which the phase difference θ is 0 to 360 degrees is divided into sections of 45 degrees, and each section changes substantially linearly with respect to the phase difference θ. A function whose value increases monotonously is set as a set of interval functions using tan θ or cot θ.

  Specifically, in each section where the phase difference θ is 90 to 135 degrees, 225 to 270 degrees, and 270 to 315 degrees, an interval function including cot θ is used, and the phase difference θ is 135 to 180 degrees, 180 to 225 degrees, 315 An interval function including tan θ is used in each interval of ˜360 degrees. That is, in the section where the phase difference θ is 90 to 135 degrees, 2-cot θ, in the section where the phase difference θ is 225 to 270 degrees and 270 to 315 degrees, 6-cot θ, and the phase difference θ is 135 to 180 degrees and 180 to 225 degrees. 4 + tan θ and 8 + tan θ are used in the section where the phase difference θ is 315 to 360 degrees. In this way, by dividing the phase difference θ into sections of 45 degrees and assigning section functions that change almost linearly for each section, as shown in FIG. 2, a domain where the phase difference θ is 0 to 360 degrees is obtained. It is possible to set a monotonically increasing function whose value range is 0 to 8 when held. In FIG. 2, straight line A is a function value to be approximated, and curve B represents an approximate value obtained from an interval function. If the unit of the phase difference θ is radians, the interval function for each interval is as shown in Table 1. In Table 1, two adjacent sections using the same section function are described as one.

  By using the function shown in Table 1, a value corresponding to the phase difference θ on a one-to-one basis and substantially proportional to the phase difference θ can be obtained, and the distance is proportional to the phase difference θ. The function value obtained by the above can be converted into a distance by a simple proportional calculation. That is, if the function defined in Table 1 is f (θ) and the proportionality constant is k, the distance can be expressed in the form of k · f (θ). Therefore, by obtaining tan θ or cot θ, the distance Can be easily obtained.

  By the way, since cotθ is 1 / tanθ, cotθ can be obtained using the detected values A0, A1, A2, and A3. That is, tan θ is expressed as tan θ = (A 3 −A 1) / (A 2 −A 0) using the detected values A 0, A 1, A 2, and A 3, so cot θ is cot θ = (A 2 −A 0) / ( A3-A1). That is, when obtaining the function value of the interval function using the detection values A0, A1, A2, and A3, only the four arithmetic operations need be performed, and the arithmetic processing becomes very simple.

  On the other hand, since the function shown in Table 1 uses a different interval function for each interval where the phase difference θ exists, it is necessary to determine the interval where the phase difference θ exists in order to obtain the function value. Specifically, the signs of (A2-A0) and (A3-A1) and the magnitude relationship between the absolute values of both are used. For example, | A3-A1 | is smaller than | A2-A0 | because sections 0 ≦ θ <π / 4, 3π / 4 ≦ θ <5π / 4, 7π / 4 ≦ θ <2π (section name 1, 4, 5, 8), and when the absolute value magnitude relationship is reversed, the section is π / 4 ≦ θ <3π / 4, 5π / 4 ≦ θ <7π / 4 (section name 2 3, 6, 7). Further, considering the signs of (A2-A0) and (A3-A1), the phase difference θ at which (A2-A0) becomes positive is 0 <θ ≦ π / 2, 3π / 2 ≦ θ <2π. The phase difference θ in which the range (A3−A1) becomes positive is in the range of 0 <θ <π. Therefore, when these relationships are combined, an interval of 45 degrees and (A2−A0) and (A3−3) are combined. The relationship between the sign of A1) and the magnitude of the absolute value is as shown in Table 2. In Table 2, A2-A0 = Ax and A3-A1 = Ay are set.

  Since tan θ = Ay / Ax, it must be Ax ≠ 0 in the sections 1, 4, 5, and 8, whereas in the sections 2, 3, 6, and 7, since cot θ = Ax / Ay is used, Ay ≠ Must be zero.

  The arithmetic processing unit 6 of the present embodiment is configured based on the above-described principle, and is a group of detected values A0, A1, A2, and A3 detected values input from the sampling unit 5 to the arithmetic processing unit 6. Is input to the section determination unit 7 and the calculation unit 8. The section discriminating unit 7 discriminates a section using the relationship shown in Table 2 for the detection value group, and which section of the eight sections is divided into 45 degrees by the phase difference θ. Determined. On the other hand, the calculation unit 8 obtains a value corresponding to the phase difference θ by applying a function approximated by the five interval functions shown in Table 1 to the detected value group, and is determined by the interval determination unit 7. The interval function corresponding to the selected interval is selected, and the selected interval function is applied to the detected value group.

  The processing procedure of the arithmetic processing unit 6 is summarized as shown in FIG. That is, when four detection values A0, A1, A2, A3 are input from the sampling unit 5 (S1), the sign of A3-A1 is obtained (S2), and the sign of A2-A0 is obtained (S3). Further, the size of | A3-A1 | and | A2-A0 | is determined (S4). For this determination, as shown in Table 2, a process of determining the sign of | A3-A1 |-| A2-A0 | may be used. It is possible to determine in which section of the eight sections the phase difference θ exists by the processing in step S4. That is, the processing of steps S <b> 2 to S <b> 4 corresponds to the section determination unit 7.

  Next, an interval function corresponding to the determined interval is selected (S5). The interval function is stored in advance in the calculation unit 8, and when the interval determination unit 7 determines the interval, the interval function corresponding to the interval is used in the calculation unit 8. Detection values A0, A1, A2, and A3 are substituted into the interval function selected in step S5, and a value corresponding to the phase difference θ is obtained (S6). Further, as described above, the distance to the object 3 is proportional to the phase difference θ, and the threshold values of the functions shown in Table 1 are 0 to 8, so the frequency of the modulation signal that modulates the light projected from the light source 1 Is 18.75 MHz, the value of the phase difference θ obtained by the calculation unit 8 and the distance to the object 3 substantially coincide with each other. Since the interval function is an approximate value, a slight error occurs when this result is used, but the obtained value can be used as it is if the error does not cause a problem. In the above example, tanθ, 2-cotθ, 4 + tanθ, 6-cotθ, and 8 + tanθ are used as the interval functions. However, if an appropriate coefficient is multiplied according to the modulation frequency, the modulation frequency is different. However, the output value of the calculation unit 8 can be matched with the distance. That is, the coefficient corresponding to the modulation frequency may be ρ, and ρ · tan θ, ρ (2-cot θ), and the like.

  In the above example, the arithmetic processing unit 6 uses the four detection values A0, A1, A2, and A3 to obtain the value of the function f (θ) that is substantially proportional to the phase difference θ. Since there are three unknowns included in the intensity I of light to be transmitted, the amplitude A, the component B due to ambient light, and the phase difference θ (see FIG. 15), the phase difference θ can be obtained from the three detected values. Is possible. Therefore, a case where the phase difference θ is obtained using the three detection values A0, A1, and A2 is illustrated.

As described in the related art, the detection values A0, A1, and A2 are represented by the following equations.
A0 = A ′ · cos θ + B ′
A1 = A ′ · sin θ + B ′
A2 = −A ′ · cos θ + B ′
First, let us consider creating an equation that eliminates A ′ and B ′ from these three equations and uses only the phase difference θ as a variable. B ′ can be erased by obtaining the difference between any two of the detected values A0, A1, and A2, and A ′ can be erased by dividing one of two different expressions after erasing B ′ by the other. it can.

  If the value corresponding to the tangent of the phase difference θ obtained from the four detected values A0, A1, A2, and A3 can be obtained from the three detected values A0, A1, and A2, the functions shown in Table 1 are used. f (θ) can be used. When obtaining a value corresponding to the tangent of the phase difference θ, it is necessary to eliminate A ′ by division as described above. Therefore, to obtain the tangent, the values of the sine and cosine in the same phase are required. . Since the sine and cosine must be obtained by subtraction for eliminating B ′, and the sine and cosine must be obtained in the same phase, the detected values A0, A1,. The subtraction of A2 needs to be performed at equal phase intervals. Since there are only three detection values A0, A1, and A2, they cannot be subtracted at intervals of 180 degrees as in the case of four. Therefore, in this example, subtraction is performed at intervals of 90 degrees. However, detection values at intervals of 60 degrees or 45 degrees can also be used.

Since there are two sets of detection values A0, A1, and A2 whose phases are different by 90 degrees, the detection values A0, A1, and A2 are subtracted by a combination of the following equations.
A1−A0 = A ′ (sin θ−cos θ) = A ″ · sin (θ−π / 4)
A1−A2 = A ′ (sin θ + cos θ) = A ″ · cos (θ−π / 4)
However, A ″ = (1/2) ^1/2 · A ′. That is, by using the detection values A0, A1, and A2, the following expression is obtained with respect to the phase difference θ.
tan (θ−π / 4) = (A1−A0) / (A1−A2)
Here, if Θ = θ−π / 4, the following equation is obtained.
tan Θ = (A1-A0) / (A1-A2)
Θ used in the above equation is advanced by 45 degrees with respect to the phase difference θ, but is only shifted in the time axis direction and is a function of the phase difference, so it is treated as equivalent to the phase difference θ. Hereinafter, it is referred to as a partial phase difference Θ. If the phase difference θ in Table 1 is read as the partial phase difference Θ, Table 1 can be used as it is.

  That is, the function f (Θ) can be represented by an 8-section function. However, the sections 1 to 7 of the partial phase difference Θ correspond to the sections 2 to 8 of the true phase difference θ, and the section 8 of the partial phase difference Θ has no section corresponding to the true phase difference θ. In addition, the value of the interval function obtained in the intervals 1 to 7 of the partial phase difference Θ is smaller by 1 than the values of the intervals 2 to 8 of the true phase difference θ. Therefore, 1 is added to the value of the interval function obtained by applying the partial phase difference Θ, and instead of the function f (θ) corresponding to the true phase difference θ, f (Θ) +1 (= f (θ −π / 4) +1) is used. That is, in the range where the partial phase difference Θ is 0 to 315 degrees, the function f (Θ) +1 is 1 to 8, and the same value as the interval function f (θ) in the range where the true phase difference θ is 45 to 360 degrees. become.

  However, the section set in Table 1 for the true phase difference θ is in the range of 0 to 360 degrees, and the section 8 of the partial phase difference Θ corresponds to 360 to 405 degrees in the true phase difference θ. The section 8 of Θ deviates from the range of the phase difference θ. However, a phase difference θ of 360 to 405 degrees is equivalent to a phase difference θ of 0 to 45 degrees. On the other hand, when the partial phase difference Θ is used, the value corresponding to the section 1 of the section function f (θ) cannot be obtained in the sections 1 to 8 of the partial phase difference Θ. Therefore, attention is paid to the fact that the interval function in the interval 8 of the partial phase difference Θ is obtained by adding 8 to the interval function in the interval 1, and when the partial phase difference Θ is the interval 8, subtract 8 from the value of the interval function. 1 is added. That is, when the partial phase difference Θ is the section 8, 7 is subtracted from the value of the section function.

  Table 2 is used for the classification of the sections related to the partial phase difference Θ. However, the phase difference θ is read as the partial phase difference Θ, and Ax = A1-A2 and Ay = A1-A0.

(Embodiment 2)
In the first embodiment, eight sections are discriminated by the section discriminating unit 7, but the calculation unit 8 uses five section functions to calculate. Therefore, the error is slightly larger near the center of each section. In the present embodiment, an example in which an error is reduced by using an interval function having better linearity with respect to the phase difference θ than the interval function used in the first embodiment will be described. That is, different interval functions are applied to 8 intervals. Each section and the section function have the relationship shown in Table 3.

However,
t ⁺ = (1 + tan θ) / (1−tan θ)
t ⁻ = (1−tan θ) / (1 + tan θ)
It is. The interval functions shown in Table 3 are set to be approximately symmetrical with respect to each interval function shown in Table 1 with a straight line connecting the origin and coordinates (360 degrees, 8), and the average of both is obtained. It is a thing. In other words, the section function that is the target across the straight line with respect to Table 1 is obtained by translating the section functions of the adjacent sections as shown in Table 4.

Since tan (θ + π / 4) = − cot (θ−π / 4) = t ⁺ and tan (θ−π / 4) = − cot (θ + π / 4) = − t ⁻ , the section in Table 4 The interval functions 1 to 9 are 1-t ⁻ , 1-t ⁻ , 3 + t ⁺ , 3 + t ⁺ , 5-t ⁻ , 5-t ⁻ , 7 + t ⁺ , and 7 + t ⁺ , respectively. In other words, if the interval functions in Table 4 are used, approximation can be performed with four types of interval functions.

By the way, the interval function of Table 1 and the interval function of Table 4 both have a larger difference from the straight line at the center of the interval than at both ends. On the other hand, when an average value of the interval function of Table 1 and the interval function of Table 4 is obtained, an interval function that substantially matches the straight line can be set. For example, when the average of the interval functions is obtained for interval 1, (tan θ + 1−t ⁻ ) / 2 is obtained, and the interval function in interval 1 in Table 3 is obtained. Similarly, when the average of the interval functions of Table 1 and Table 4 is obtained for each interval, the interval function of Table 3 is obtained. Therefore, by using the interval function shown in Table 3, the error at the center of the interval is reduced, and it is possible to substantially match the straight line. For example, in section 1, as shown in FIG. 4, when the function value to be approximated is a straight line A, using the section function in Table 1 gives a curve B, but using the section function in Table 3, curve H It can be seen that it almost coincides with the straight line a.

Further, since tan θ = (A3−A1) / (A2−A0),
t ⁺ = (A2-A0) + (A3-A1) / (A2-A0)-(A3-A1)
t ⁻ = (A2−A0) − (A3−A1) / (A2−A0) + (A3−A1)
As in Table 2, if A2-A0 = Ax and A3-A1 = Ay are set,
t ⁺ = (Ax + Ay) / (Ax−Ay)
t ⁻ = (Ax−Ay) / (Ax + Ay)
become.

That is, t ⁺ and t ⁻ can be represented by the values Ax and Ay used for section discrimination in the section discriminator 7, and since tan θ = Ay / Ax, the section function can be represented by Ax and Ay. it can. Therefore, as shown in FIG. 5, the arithmetic processing unit 6 is provided with a pre-operation unit 9 that performs the calculation of (A3-A1) and (A2-A0) before the section determination unit 7 and the calculation unit 8. If the discrimination of the section in the discrimination unit 7 and the calculation of the approximate value using the interval function in the calculation unit 8 are performed using the calculation result of the prefix calculation unit 9, the detected values A0, A1, A2 , The amount of calculation is reduced as compared with the case of calculating using A3 as it is. The prefix calculation unit 9 can also be used in the configuration of the first embodiment, and tan θ and cot θ in the calculation unit 8 may be expressed using Ax and Ay used for section determination in the section determination unit 7. Further, when the interval function in the present embodiment is used, the amount of calculation increases compared to the interval function calculation used in the first embodiment, but only the four arithmetic operations of the detected values A0, A1, A2, and A3. Compared with the calculation according to, the calculation amount is very small and the load of calculation processing is small, and it is not necessary to use a large storage area or perform interpolation calculation as in the case of using a data table.

  The reason why the coefficient is ½ (divided by 2) in each interval function in Table 3 is simply that the average value of the two interval functions is a new interval function, and is not necessarily 1/2. There is no need. When the coefficient is 1/2, the distance to the object 3 and the output value of the calculation unit 8 substantially coincide with each other when the modulation frequency is 18.75 MHz. In the case of other modulation frequencies, an operation for multiplying the output value by a coefficient is required in order to convert the output value into a distance. In this case, the coefficient of the interval function to be used may be set so that the output value of the calculation unit 8 becomes the distance value as it is as another value in consideration of the modulation frequency instead of ½.

(Embodiment 3)
In the first and second embodiments, the configuration including only one photodetecting element 2 has been described. However, the first and second embodiments are also used when using an image sensor in which a plurality of photodetecting elements 2 are arranged on lattice points of a planar lattice. The technique described in the above can be applied. This type of image sensor is known as a CCD image sensor, a CMOS image sensor, or the like, and a light receiving period in which light is received in the light detection element 2 and a take-out period in which a light reception output is taken out are controlled by external signals. Therefore, it is possible to obtain the detection values A0, A1, A2, and A3 as the output of the image sensor without providing a sampling unit outside the image sensor by controlling the light receiving period and the extraction period of the image sensor by an external signal. That is, the function corresponding to the sampling unit 6 described in the first and second embodiments is built in the image sensor.

  In the image sensor, since the electric charge generated by the light detection element 2 during the light receiving period is taken out as a light receiving output during the extraction period, it is desirable to increase the sensitivity to light during the light receiving period and decrease the sensitivity to light during the extraction period. Furthermore, the light receiving period needs to be set at a timing that is 90 degrees out of phase with respect to the modulation signal, and light reception is performed so that four detection values A0, A1, A2, and A3 are obtained within one period of the modulation signal. If the timing of the period is set, the amount of received light corresponding to each detection value A0, A1, A2, A3 is very small, and a large received light output cannot be obtained. In particular, if the amount of received light is small, the S / N ratio of the received light output is reduced due to shot noise generated inside the image sensor, resulting in a decrease in distance measurement accuracy. Therefore, in the present embodiment, a configuration is adopted in which each detected value A0, A1, A2, A3 is associated with a charge accumulated in a plurality of periods of the modulation signal. Therefore, the image sensor 10 used in the present embodiment integrates the sensitivity adjustment unit 11 that adjusts the sensitivity of the light detection element 2 and the charges generated by the light detection element 2 over a desired period as shown in FIG. The charge accumulating unit 12 and the charge extracting unit 13 that extracts the charges accumulated in the charge accumulating unit 12 from the image sensor 10 are provided.

  Hereinafter, as a specific configuration of the sensitivity adjustment unit 11, the charge accumulation unit 12 is provided separately from the light detection element 2, and the ratio of the charge given to the charge accumulation unit 12 among the charges generated by the light detection element 2 is adjusted. The amount of charge accumulated in the charge accumulating unit 12 can be determined by changing the area (size) of the portion where the charge accumulating unit 12 is substantially provided in the photodetecting element 2 and substantially generating charges in the photodetecting element 2. The technology to adjust. If the sensitivity adjusting unit 11 is provided and the sensitivity is increased only during a desired period, only the charge in the target period is taken out, so that it is substantially sampled, and the sampling unit in the first and second embodiments. Six functions can be realized by the sensitivity adjustment unit 11.

  In order to adjust the ratio of charges applied to the charge accumulation unit 12 provided separately from the photodetection element 2, a technique for adjusting the pass rate of charges from the photodetection element 2 to the charge accumulation unit 12, and from the photodetection element 2 There are a technique for adjusting the discard rate for discarding charges and a technique for adjusting both the passage rate and the discard rate.

  In the technique of adjusting the pass rate and the discard rate in the sensitivity adjusting unit 11, as shown in FIG. 7, a gate electrode 11a is provided between the photodetecting element 2 and the charge accumulating unit 12, and the pass applied to the gate electrode 11a. By changing the voltage, the movement (that is, the pass rate) of charges from the photodetecting element 2 to the charge accumulating unit 12 is controlled. Further, by providing the charge discarding part 11c and changing the discarding voltage applied to the discarding electrode 11b attached to the charge discarding part 11c, the movement of charges from the photodetecting element 2 to the charge discarding part 11c (that is, the discard rate) To control. The charge integration units 12 are provided so as to correspond one-to-one for each photodetecting element 2, and the charge discarding units 11c are provided so as to correspond to the plurality of photodetecting elements 2 so as to correspond one-to-many. In the illustrated example, all of the light detection elements 2 of the light detection elements 2 share a set of waste electrode 11b and charge disposal portion 11c.

  In order to control the sensitivity, it is conceivable to control only the pass rate from the photodetecting element 2 to the charge accumulating unit 12 without discarding the charge from the photodetecting element 2, but the charge must be discarded. For example, since charges remain in the photodetecting element 2 for a while, unnecessary residual charges among the charges generated by the photodetecting element 2 are mixed as noise components in the used charges (hereinafter referred to as signal charges). Therefore, in this embodiment, in order to prevent the residual charge from being mixed into the signal charge, not only the passing voltage applied to the gate electrode 11a but also the discard voltage applied to the discard electrode 11b is controlled.

  In order to control the sensitivity using the gate electrode 11a and the waste electrode 11b, the charge generated by the photodetecting element 2 can pass through the charge accumulating unit 12 by keeping the passing voltage applied to the gate electrode 11a constant. The waste voltage is applied to the waste electrode 11b so that the charge is transferred from the light detection element 2 to the charge disposal unit 11c except for the period in which the charge used for the signal charge is generated among the charges generated by the light detection element 2. Apply. In short, the signal is not discarded to the charge discarding unit 11c only during the period in which the charge used as the signal charge is generated in the photodetecting element 2, and the signal is discarded to the charge discarding unit 11c in the other period. Only charges generated during a period of use as charges are accumulated in the charge accumulation unit 12.

  Now, it is assumed that the intensity of light emitted from the light source 1 to the space is modulated by the modulation signal as shown in FIG. The charge accumulating unit 12 accumulates charges corresponding to detection values A0, A1, A2, and A3 in a specific section synchronized with the modulation signal in a plurality of periods (tens of thousands to hundreds of thousands) of the modulation signal. Then, the accumulated charges are taken out and accumulated in the next section. For example, when charges corresponding to the detection value A0 are accumulated for tens of thousands of cycles of the modulation signal, the signal charge corresponding to the detection value A0 is once taken out to the outside, and thereafter, the charge corresponding to the detection value A1 is converted to tens of thousands of modulation signals. Accumulate about the period.

  FIG. 8 shows a state in which charges corresponding to the detected value A0 are accumulated, and the passing voltage applied to the gate electrode 11a is kept constant as shown in FIG. 8B. Further, as the charge corresponding to the detection value A0, the charge generated by the light detection element 2 in the interval where the phase of the modulation signal is 0 to 90 degrees is employed. That is, a waste voltage is applied to the waste electrode 11b so that the charge generated by the photodetecting element 2 is an unnecessary charge in the section where the phase of the modulation signal is 90 to 360 degrees as shown in FIG. 8C. . By this control, signal charges corresponding to a desired light receiving period T0 can be accumulated in the charge accumulation unit 12 as shown in FIG. The processing shown in FIG. 8 is performed for tens of thousands to hundreds of thousands of cycles of the modulation signal, and the signal charge obtained in the charge accumulating unit 12 during this period is taken out through the charge extracting unit 23 as a light receiving output corresponding to the detected value A0. . The charge extraction unit 23 has the same configuration as a vertical transfer register and a horizontal transfer register in a CCD image sensor or a CMOS image sensor.

  The electric charge extracted from the electric charge extraction unit 23 is given as an image signal to the image generation unit 24. The image generation unit 24 corresponds to the detection values A0, A1, A2, and A3 using the techniques described in the first and second embodiments. The distance from the received light output to the object 3 in the target space is calculated. Since the distance to the object 3 is obtained for each light detection element 2, the image generation unit 24 calculates the distance to the object 3 in each direction corresponding to each light detection element 2, and obtains 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 value of the pixel corresponding to each direction of the target space is a distance value.

  In the above control, a passing voltage that is a constant voltage is applied to the gate electrode 11a during the period in which the discarding voltage is applied to the discarding electrode 11b, but the magnitude relationship between the discarding voltage and the passing voltage is appropriately determined. If set, it is possible to prevent the signal charge from being almost accumulated in the charge accumulation unit 12 during the period in which the unnecessary charge is discarded. Further, the signal charges are accumulated for tens of thousands to hundreds of thousands of cycles of the modulation signal in order to increase the sensitivity by increasing the amount of charges to be accumulated. If the modulation signal is set to 20 MHz, for example, Even if signal charges are taken out at 30 frames / second, integration of several hundred thousand cycles or more is possible.

  As described above, the charge discarding unit 11c including the discard electrode 11b is provided, and unnecessary charges that are not used as signal charges out of the charges generated by the light detection element 2 are actively discarded to the charge discarding unit 11c. In the photodetecting element 2, most of the charge generated by the photodetecting element 2 during the period when no signal charge is applied to the charge accumulating unit 12 is discarded as unnecessary charge, and noise components are greatly mixed into the signal charge. To be suppressed.

  In the above-described example, a period in which the discard voltage is not applied by providing a period in which the discard voltage is applied to the discard electrode 11b and a period in which the discard voltage is not applied to the discard electrode 11b in the period in which the passing voltage that is a constant voltage is applied to the gate electrode 11a. In FIG. 9, the charge generated in the photodetecting element 2 is used as the signal charge. As shown in FIG. 9, the period for applying the passing voltage to the gate electrode 11a and the period for applying the discarding voltage to the discarding electrode 11b overlap. You may control so that it may not.

  FIG. 9 shows the operation when signal charges corresponding to the detected value A0 are integrated. FIG. 9A shows a modulation signal for modulating the intensity of light emitted to the space from the light source 1, and the gate electrode 11a has a timing corresponding to the detection value A0 as shown in FIG. 9B. Apply the passing voltage with. The period during which the pass voltage is applied to the gate electrode 11a is set from 0 degrees to a certain period (0 to 90 degrees in the illustrated example) in the phase of the modulation signal. In this period, the charge from the photodetecting element 2 to the charge integration unit 12 is set. Can be moved. On the other hand, as shown in FIG. 9C, a discard voltage is applied to the waste electrode 11b in a period other than the period in which the signal charge corresponding to the detection value A0 is accumulated in the charge accumulation unit 12, and in the period other than the period in which the signal charge is accumulated. The charges generated by the light detection element 2 are discarded as unnecessary charges in the charge discarding unit 11c. Such control makes it possible to extract signal charges corresponding to the detection value A0 as shown in FIG.

  In the control shown in FIG. 9, the period during which the pass voltage is applied to the gate electrode 11a is different from the period during which the waste voltage is applied to the discard electrode 11b. Therefore, as shown in the control example in FIG. The magnitude of the passing voltage and the discarding voltage can be controlled independently without considering the magnitude relationship with the discarding voltage, and as a result, the passing voltage and the discarding voltage can be easily controlled. Control of the sensitivity, which is the ratio of taking in signal charges with respect to the amount of received light, is facilitated, and control of the ratio of discarding unnecessary charges out of the charges generated by the light detection element 2 is facilitated. Further, in the control example shown in FIG. 9, the period in which the signal charge is accumulated in the charge accumulation unit 12 is defined by the passing voltage applied to the gate electrode 11a, so the period in which the waste voltage is applied to the waste electrode 11b is shortened. For example, it is possible to apply the waste voltage to the waste electrode 11b only during a predetermined period immediately before applying the pass voltage to the gate electrode 11a.

  If the control shown in FIG. 9 is performed, the charge generated by the light detection element 2 is discarded as an unnecessary charge during the period when the charge generated by the light detection element 2 is not integrated as a signal charge in the charge integration unit 12. Mixing of noise components into the signal charge is greatly suppressed.

  As an example of controlling the passing voltage and the discarding voltage, as shown in FIG. 10, when the discarding voltage applied to the discarding electrode 11b is kept at a constant voltage, a part of the charge generated by the light detection element 2 is always discarded. There is also. In the control example of FIG. 10, a period during which the passing voltage is applied to the gate electrode 11 a and a period during which the passing voltage is not applied are provided, and the period during which the passing voltage is applied is defined as a period during which signal charges are accumulated in the charge accumulation unit 12.

  FIG. 10 shows an operation when signal charges corresponding to the detected value A0 are integrated. FIG. 10A shows a modulation signal that modulates the intensity of light emitted from the light source 1 to the space, and the gate electrode 11a provided in the charge accumulating unit 12 has a structure as shown in FIG. A passing voltage is applied during a period corresponding to the detection value A0, and the charge generated in the light detection element 2 is accumulated in the charge accumulation unit 12 as a signal charge corresponding to the detection value A0. That is, the period during which the pass voltage is applied to the gate electrode 11a is set from 0 degree to a certain period (0 to 90 degrees in the illustrated example) in the phase of the modulation signal, and from the photodetecting element 2 to the charge integration unit 12 in this period. Can be transferred. On the other hand, as shown in FIG. 10C, a constant voltage discard voltage, which is a DC voltage, is always applied to the waste electrode 11b, and a part of the charge generated by the light detection element 2 is always discarded as an unnecessary charge. Discard in part 11c. In the above-described control, since the passing voltage is applied to the gate electrode 11a only during the period in which the signal charge is accumulated in the charge accumulation unit 12, the signal charge corresponding to the detection value A0 is taken out as shown in FIG. Is possible.

  In the control shown in FIG. 10, a constant voltage discard voltage is applied to the discard electrode 11b regardless of whether or not a pass voltage is applied to the gate electrode 11a. Unnecessary charges that have not been accumulated as signal charges in the charge accumulation unit 12 are discarded as discard charges in the charge discard unit 11c. Here, even in a period in which a part of the charge generated by the light detection element 2 is accumulated in the charge accumulation unit 12 as a signal charge, the disposal of the charge from the light detection element 2 to the charge discarding unit 11c continues. In order to properly accumulate the signal charges in the charge accumulation unit 12, it is necessary to consider the magnitude relationship between the passing voltage and the discard voltage. However, since the discard voltage is a constant voltage and is always applied to the discard electrode 11b, in actuality, it is sufficient to control only the passing voltage, and the control itself is easy.

  The photodetecting element 2 including the sensitivity adjusting unit 11 illustrated in FIG. 7 can be realized by a CCD image sensor including an overflow drain. Any charge transfer method may be used in the CCD image sensor, and any of an interline transfer (IT) method, a frame transfer (FT) method, and a frame interline transfer (FIT) method may be used.

  FIG. 11 shows a configuration of an interline transfer type CCD image sensor having a vertical overflow drain. The illustrated example is a two-dimensional image sensor in which a plurality of photodiodes 41 serving as the light detection elements 2 are arranged in a horizontal direction and a vertical direction (3 × 4 in the figure), and the photodiodes 41 are arranged in the vertical direction. A vertical transfer register 42 made of CCD is provided on the right side of each column, and a horizontal transfer register 43 made of CCD is provided below the area where the photodiode 41 and the vertical transfer register 42 are arranged. The vertical transfer register 42 includes two transfer electrodes 42 a and 42 b for each photodiode 41, and the horizontal transfer register 43 includes two transfer electrodes 43 a and 43 b for each vertical transfer register 42.

  The photodiode 41, the vertical transfer register 42, and the horizontal transfer register 43 are formed on one semiconductor substrate 40, and the photodiode 41, the vertical transfer register 42, and the horizontal transfer register 43 are formed on the main surface of the semiconductor substrate 40. An overflow electrode 44 which is an aluminum electrode is provided so as to directly contact the semiconductor substrate 40 without going through an insulating film over the entire circumference of the semiconductor substrate 40 so as to surround the whole. If an appropriate disposal voltage that is positive with respect to the semiconductor substrate 40 is applied to the overflow electrode 44, electrons (charges) generated by the photodiode 41 are discarded through the overflow electrode 44. The overflow electrode 44 functions as the discard electrode 11b because a discard voltage is applied when discarding unnecessary charges among the charges generated in the photodiode 41 which is the light detection element 2, and applies the discard voltage to the overflow electrode 44. The power supply functions as a charge discarding unit 11c that discards electrons (charges) generated by the light detection element 2. The surface of the semiconductor substrate 40 is covered with a light shielding film 46 (see FIG. 12) except for the portion corresponding to the photodiode 41.

With respect to the CCD image sensor shown in FIG. 11, a portion related to one photodiode 41 is cut out and shown in FIG. An n-type semiconductor is used for the semiconductor substrate 40, and a well region 31 made of a p-type semiconductor is formed in a region straddling the photodiode 41 and the vertical transfer register 42 on the main surface of the semiconductor substrate 40. The well region 31 is formed so that the thickness dimension of the region corresponding to the vertical transfer register 42 is larger than the region corresponding to the photodiode 41. An n ^{+ -type} semiconductor layer 32 is provided in a region corresponding to the photodiode 41 in the well region 31, and the photodiode 41 is formed by a pn junction between the well region 31 and the n ^{+ -type} semiconductor layer 32. A surface layer 33 made of a p ^{+ type} semiconductor is laminated on the surface of the photodiode 41. The surface layer 33 is provided for the purpose of controlling the vicinity of the surface of the n ^{+ -type} semiconductor layer 32 so as not to be a charge passage path when the charge generated by the photodiode 41 is moved to the vertical transfer register 42. Such a structure is known as a buried photodiode.

An integrated transfer layer 34 made of an n-type semiconductor is overlaid in a region corresponding to the vertical transfer register 42 in the well region 31. The surface of the integrated transfer layer 34 and the surface of the surface layer 33 are substantially in the same plane, and the thickness dimension of the integrated transfer layer 34 is larger than the thickness dimension of the surface layer 33. The integrated transfer layer 34 is in contact with the surface layer 33, but a separation layer 35 made of a p ^{+ type} semiconductor having the same impurity concentration as that of the surface layer 33 is interposed between the integrated transfer layer 34 and the n ^{+ type} semiconductor layer 32. Transfer electrodes 42 a and 42 b are disposed on the surface of the integrated transfer layer 34 with an insulating film 45 interposed therebetween. Two transfer electrodes 42a and 42b are provided for each photodiode 41, and one of the two transfer electrodes 42a and 42b is formed wider than the other in the vertical direction. Specifically, as shown in FIG. 13, of the two transfer electrodes 42a and 42b corresponding to one photodiode 41, the narrow transfer electrode 42b is formed in a flat plate shape, and the wide transfer electrode 42a. Is a flat plate portion arranged on the same plane as the narrow transfer electrode 42b and disposed between the pair of transfer electrodes 42b, and from both ends in the vertical direction of the flat plate portion (left and right direction in FIG. 13). And a curved portion that extends and overlaps the transfer electrode 42b. Here, the insulating film 45 is formed of SiO ₂ , the transfer electrodes 42 a and 42 b are formed of polysilicon, and the transfer electrodes 42 a and 42 b are insulated from each other through the insulating film 45. Further, the surface of the light detection element 2 is covered with a light shielding film 46 except for a portion where light is incident on the photodiode 41. In the well region 31, the region corresponding to the vertical transfer register 42 and the integrated transfer layer 34 are formed over the entire length of the vertical transfer register 42. Therefore, the integrated transfer layer 34 has a wide transfer electrode 42a and a narrow transfer electrode 42b. And are alternately arranged.

  In the light detection element 2 described above, the photodiode 41 corresponds to the light detection element 2, the transfer electrode 42a corresponds to the gate electrode 11a, the overflow electrode 44 corresponds to the discard electrode 11b, and the vertical transfer register 42 corresponds to the charge integration unit. 12 and a part of the charge extraction unit 23. Further, the horizontal transfer register 43 also becomes a part of the charge extraction unit 23. That is, if light enters the photodiode 41, a charge is generated, and the ratio of the charge generated as a signal charge to the vertical transfer register 42 among the charges generated by the photodiode 41 is equal to the passing voltage applied to the transfer electrode 42a and the overflow. It can be determined according to the relationship with the waste voltage applied to the electrode 44. When a passing voltage is applied to the transfer electrode 42a, a potential well is formed in the integrated transfer layer 34, and the depth of the potential well can be controlled by controlling the passing voltage. Therefore, by controlling the depth of the potential well and the time during which the passing voltage is applied, the ratio of charges delivered from the photodiode 41 to the vertical transfer register 42 can be adjusted. Further, if the discard voltage applied to the overflow electrode 44 is controlled, the potential gradient between the photodiode 41 and the semiconductor substrate 40 can be controlled. Therefore, if the potential gradient and the time for applying the discard voltage are controlled. The rate of charge delivered to the vertical transfer register 42 can be adjusted. The passing voltage and the discard voltage may be controlled as in the control examples shown in FIGS.

  The signal charge delivered from the photodiode 41 to the vertical transfer register 42 is a signal corresponding to the detection values A0, A1, A2, and A3 in each of the four detection values A0, A1, A2, and A3 described above. It is read each time charge is accumulated. For example, when the signal charge corresponding to the detection value A0 is accumulated in the potential well formed corresponding to each photodiode 41, the signal charge is read, and then the signal charge corresponding to the detection value A1 is accumulated in the potential well. Then, the operation of reading the signal charge again is repeated. Note that the period for collecting signal charges corresponding to the detection values A0, A1, A2, and A3 is set to be equal.

  Among the control examples described above, in the control example shown in FIG. 8, the charge (electrons) generated by the light detection element 2 (photodiode 41) is always delivered to the charge accumulation unit 12 (vertical transfer register 42). Therefore, the charges accumulated in the charge accumulating unit 12 are not necessarily mixed with the charges generated during the period in which the target detection values A0, A1, A2, A3 are obtained, but also the charges generated during the non-target period. become. Now, in the sensitivity adjustment unit 11, the sensitivity in the period for generating the charges corresponding to the detection values A0, A1, A2, and A3 is α, and the sensitivity in the other periods is β, and the light detection element 2 is proportional to the detection value. It shall generate an electric charge. Under this condition, the charge accumulating unit 12 that accumulates charges corresponding to the detection value A0 is proportional to αA0 + β (A1 + A2 + A3) + βAx (Ax is a detection value other than the period during which the detection values A0, A1, A2, and A3 are obtained). Charges proportional to αA2 + β (A0 + A1 + A3) + βAx are accumulated in the charge accumulation unit 12 that accumulates charges and accumulates charges corresponding to the detection value A2. As described above, when obtaining the phase difference ψ, (A2−A0) is obtained, and when a value corresponding to (A2−A0) is obtained from the charge (light reception output) accumulated in the charge accumulation unit 13 (α −β) (A2−A0), and similarly, the value corresponding to (A3−A1) becomes (α−β) (A3−A1), and the phase difference ψ = (A2−A0) / (A3-A1) theoretically has the same value regardless of the presence or absence of charge, and the phase difference ψ to be obtained is the same even if charge is mixed.

  In the configuration example described above, a CCD image sensor is used for the light detection element 2, and the amount of charge passed through the charge accumulation unit 12 provided separately from the light detection element 2 and the amount of charge discarded in the charge disposal unit 11 c Although the example in which the sensitivity adjustment unit 11 is configured by controlling at least one of them is shown, in the configuration example shown below, the charge integration unit 12 is provided in the light detection element 2 and the size of the charge integration unit 12 is changed. Thus, it functions as the sensitivity adjustment unit 11.

  A specific example of the light detection element 2 will be described below. In the configuration shown in FIG. 14, a plurality of (for example, 100 × 100) photodetecting elements 2 are formed on a single semiconductor substrate. One photodetecting element 2 has a configuration in which a plurality (five in the figure) of control electrodes 23 are arranged on a semiconductor layer 21 to which impurities are added via an insulating film 22 made of an oxide film. In the illustrated example, the direction in which the electrodes are arranged (left-right direction) is the vertical direction, and when taking out the charge generated by the photodetecting element 2 (using electrons in this embodiment), the charge is moved vertically by the vertical transfer register. After the transfer, it is transferred in the horizontal direction using a horizontal transfer register. That is, the charge extraction unit 23 is configured by the vertical transfer register and the horizontal transfer register. As the configuration of the vertical transfer register and the horizontal transfer register, the same configuration as the interline transfer (IT) method, the frame transfer (FT) method, and the frame interline transfer (FIT) method in the CCD image sensor can be adopted.

  That is, if the respective photodetecting elements 2 arranged in the vertical direction share a continuous semiconductor layer 21 and the semiconductor layer 21 is used as a vertical transfer register, the semiconductor layer 21 is used as both the photodetecting element 2 and the charge transfer path. The charge can be transferred in the vertical direction in the same manner as in the FT type CCD image sensor, and if the charge is transferred from the photodetecting element 2 to the vertical transfer register via the transfer gate, the IT Charges can be transferred in the same manner as in the CCD image sensor of the system or FIT system.

  As described above, the semiconductor layer 21 is doped with impurities, the main surface of the semiconductor layer 21 is covered with the insulating film 22 made of an oxide film, and a plurality of control electrodes 23 are formed on the semiconductor layer 21 via the insulating film 22. Is arranged. This light detection element 2 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 2. 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 irradiated to the target space from the light source 1 is 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. 10 shows only a region corresponding to one photodetecting element 2, and a plurality of regions having the structure shown in FIG. 14 are arranged on the semiconductor substrate (not shown) and the charge is charged. A structure to be the extraction portion 23 is provided. The vertical transfer register provided as the charge extraction unit 23 is assumed to transfer charges in the left-right direction in FIG. 14, 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 2 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 the sensitivity in the sensitivity adjusting unit 11. For example, when the control voltage + V is applied to three control electrodes 23 as shown in FIG. 14A 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, the area of the potential well 24 is larger in the state of FIG. 14A, so that the amount of light is the same as that in the state of FIG. 14B. As a result, the ratio of charges that can be used increases, and the sensitivity of the light detection element 2 is substantially increased. Thus, it can be said that the photodetecting element 2 and the sensitivity adjusting unit 11 are configured by the semiconductor layer 21, the insulating film 22, and the control electrode 23. Since the potential well 24 holds charges generated by light irradiation, it functions as the charge accumulation unit 12.

  As described above, in order to extract charges from the potential well 24, the same technique as that of the CCD image sensor is employed. For example, when the photodetector 2 is used as a vertical transfer register, after the electrons e are accumulated in the potential well 24, a control voltage having a different application pattern from that at the time of charge accumulation is applied to the control electrode 23. Can be transferred in one direction (for example, in the right direction in the figure). Alternatively, it is possible to adopt a configuration in which charges are transferred from the photodetecting element 2 to a vertical transfer register provided separately from the photodetecting element 2 via a transfer gate. Charge is transferred from the vertical transfer register to the horizontal transfer register, and the charge transferred to the horizontal transfer register is taken out of the photodetector 2 from an electrode (not shown) provided on the semiconductor substrate.

  The sensitivity adjustment unit 11 in the configuration shown in FIG. 14 switches the size (area) of the signal charge accumulation region (that is, the charge accumulation unit 12) into two levels of large and small, thereby increasing the sensitivity of the light detection element 2 in two levels. And the sensitivity is increased only during the period when the photodetecting element 2 is to generate a charge corresponding to one of the detection values A0, A1, A2, and A3 (the area for generating the charge is increased). In other periods, low sensitivity. The period of high sensitivity and the period of low sensitivity are set in synchronization with the modulation signal that drives the light source 1. Specifically, in a specific section (specific phase section) synchronized with the modulation signal, the charge generation area is increased by increasing the area for generating charges, and the other sections other than the specific section are integrated. The charge generated by the photodetecting element 2 is accumulated by reducing the area for generating the charge. That is, in the photodetecting element 2, a function for accumulating charges and a function for accumulating charges are alternately realized. Here, accumulation means collecting electric charges, and accumulation means holding electric charges. In other words, in the configuration example shown in FIG. 14, the charge generated by the light detection element 2 during the charge accumulation period is changed by changing the size (area) of the charge accumulation unit 12 provided in the light detection element 2. The integration rate of the charge generated by the photodetecting element 2 is reduced during the charge accumulation period.

  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 2 through the charge extraction unit 23. The reason why charges are integrated over a plurality of periods of the modulation signal is that the period in which the photodetecting element 2 generates usable charges within one period of the modulation signal is short (for example, the frequency of the modulation signal is 20 MHz). This is because the generated charge is small. That is, by integrating charges for a plurality of periods of the modulation signal, signal charges (charges corresponding to light emitted from the light source 1) and unnecessary charges (external light components and shots generated inside the light detection element 2). A large signal-to-noise ratio can be obtained, and a large SN ratio can be obtained.

  By the way, if the charges corresponding to the detection values A0, A1, A2, and A3 of the four sections necessary for obtaining the phase difference ψ are generated by one photodetecting element 2, the resolution with respect to the line-of-sight direction becomes high. The operation of accumulating charges for the detection values A0, A1, A2, and A3 in one section and extracting the received light output and then accumulating charges for the detection values A, A1, A2, and A3 in the next section are repeated. Since the time difference between the times when the detection values A0, A1, A2, and A3 are obtained increases, the error of the phase difference ψ may increase. On the other hand, if the charges corresponding to the detection values A0, A1, A2, and A3 are generated by the four light detection elements 2, the time difference for obtaining the charges corresponding to the detection values A0, A1, A2, and A3 is small. However, a shift occurs in the line-of-sight direction for obtaining the charges in the four sections, and the resolution in the line-of-sight direction decreases. Therefore, a configuration may be adopted in which two types of charges corresponding to the detection values A0, A1, A2, and A3 are generated in one period of the modulation signal by using two light detection elements 2. That is, two light detection elements 2 may be used as a set, and light from the same line of sight may be incident on the two light detection elements 2 in the set.

  By adopting this configuration, the resolution in the line-of-sight direction can be made relatively high, and the time difference for generating charges corresponding to the detection values A0, A1, A2, and A3 can be reduced. That is, by reducing the time difference for generating the charges corresponding to the detection values A0, A1, A2, and A3, the distance detection accuracy of the object 3 moving in the target space can be kept relatively high. Can do. In this configuration, the resolution in the line-of-sight direction is lower than that in the case where charges corresponding to the four types of detection values A0, A1, A2, and A3 are generated by one photodetecting element 2, but the resolution in the line-of-sight direction Can be improved by downsizing the light detecting element 2 or designing a light receiving optical system (not shown) disposed in the light incident path to the image sensor.

  The operation will be specifically described below. In the example shown in FIG. 14, an example is shown in which five control electrodes 23 are provided for one photodetecting element 2, but the two control electrodes 23 on both sides are charged with electrons (electrons) by the photodetecting element 2. e) is used to form a barrier for preventing the electric charge from flowing out to the adjacent photodetecting element 2, and when two photodetecting elements 2 are used as a set, Since a barrier is formed by any one of the light detection elements 2 between the potential wells 24 of the adjacent light detection elements 2, it is sufficient to provide three control electrodes 23 for each light detection element 2. become. With this configuration, the occupation area per one of the light detection elements 2 is reduced, and it is possible to suppress a decrease in resolution in the line-of-sight direction while using the two light detection elements 2 as a set.

  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 1 in front of the light detection element 2. Further, the interval function is not limited to the above example, and can be set as appropriate depending on the waveform of the modulation signal, the timing of the light receiving period, and the like.

1 is a block diagram illustrating a first embodiment. It is operation | movement explanatory drawing same as the above. It is a flowchart which shows the process sequence of the arithmetic processing part in the same as the above. It is operation | movement explanatory drawing same as the above. 6 is a block diagram illustrating an arithmetic processing unit used in Embodiment 2. FIG. FIG. 6 is a block diagram illustrating a third embodiment. It is a block diagram which shows the structural example of the sensitivity control part in the same as the above. It is explanatory drawing which shows the operation example same as the above. It is explanatory drawing which shows the other operation example same as the above. It is explanatory drawing which shows the other example of an operation same as the above. It is a top view which shows the structural example of the image sensor used for the same as the above. It is a principal part disassembled perspective view of the image sensor shown in FIG. It is sectional drawing of the AA line of FIG. It is operation | movement explanatory drawing of the principal part of the other structural example of the photon detection element used for the same as the above. It is operation | movement explanatory drawing of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light emission source 2 Photodetection element 3 Object 4 Timing control circuit 5 Sampling part 6 Operation processing part 7 Section discrimination | determination part 8 Calculation part

Claims (6)

  A light source that projects intensity-modulated light with modulated light intensity into the target space, a light detection element that receives light from the target space and obtains a light reception output according to the amount of light received, and a light reception output of the light detection element Sampling unit that extracts a detection value group consisting of a plurality of detection values by sampling at a specified timing, and intensity-modulated light and light detection emitted from the light source by substituting the detection value group into a predetermined function An arithmetic processing unit that obtains a value corresponding to a phase difference with the intensity modulated light received by the element, and the arithmetic processing unit sets a section obtained by dividing one period of the intensity modulated light into a plurality of detection value groups. A section discriminating section that discriminates a section where a phase difference exists based on a relationship between a plurality of detected values, and a section function corresponding to the section discriminated by the section discriminating section by approximating the function with a plurality of section functions set for each section. Detection value group Distance measuring device, characterized in that the assignment to and a calculation unit for obtaining a one-to-one corresponding function values to the phase difference.   The light source has a waveform of the intensity-modulated light as a sine wave, the function is a function that is linear with respect to the phase difference, and the arithmetic processing unit has three detected value groups with different phases in the intensity-modulated light at equal intervals. Using the above detection values, in the calculation unit, an interval function using at least one of a tangent and a cotangent of a value corresponding to the phase difference is set, and each of the detection value groups has different phases at equal intervals. A function value of the function is obtained by substituting at least one of the tangent and the cotangent obtained by dividing one of two differences obtained from two detection values by the other into an interval function. The distance measuring device according to claim 1.   The light source has a waveform of the intensity-modulated light as a sine wave, the function is a function that is linear with respect to a phase difference, and the arithmetic processing unit includes four detection-value groups whose phases in the intensity-modulated light are different by 90 degrees. In the calculation unit, an interval function using at least one of a tangent and a cotangent of a value corresponding to the phase difference is set, and each of the detected value groups has a phase difference of 180 degrees. A function value of the function is obtained by substituting at least one of the tangent and the cotangent obtained by dividing one of the two differences obtained from the detected values by the other into an interval function. The distance measuring device according to claim 1.   The light source has a waveform of the intensity-modulated light as a sine wave, the function is a function that is linear with respect to a phase difference, and the arithmetic processing unit has three detection-value groups whose phases in the intensity-modulated light are different at 90 degree intervals. In the calculation unit, an interval function using at least one of a tangent and a cotangent of a value corresponding to the phase difference is set, and each of the detected value groups has a phase difference of 90 degrees. A function value of the function is obtained by substituting at least one of the tangent and the cotangent obtained by dividing one of the two differences obtained from the detected values by the other into an interval function. The distance measuring device according to claim 1.   The section discriminating section is a section in which the phase difference exists using a sign of two differences obtained from two detected values having different phases in the detection value group and a magnitude of an absolute value of each difference. Are calculated in units of 45 degrees, and the calculation unit calculates each of the section functions in eight sections from 0 degrees to 360 degrees with respect to the value θ corresponding to the phase difference, tan θ, 2-cot θ, 2-cot θ, 5. The distance measuring device according to claim 2, wherein 4 + tan θ, 4 + tan θ, 6-cot θ, 6-cot θ, and 8 + tan θ are set. The section discriminating section is a section in which the phase difference exists using a sign of two differences obtained from two detected values having different phases in the detection value group and a magnitude of an absolute value of each difference. Is calculated in units of 45 degrees, and the calculation unit calculates t ⁺ = (1 + tan θ) / (1−tan θ), t ⁻ = (1−tan θ) / (1 + tan θ) with respect to the value θ corresponding to the phase difference. Then, the interval functions in 8 intervals from 0 degrees to 360 degrees are respectively (1 + tan θ−t ⁻ ) / 2, (3-cot θ−t ⁻ ) / 2, (5-cot θ + t ⁺ ) / 2, (7 + tan θ + t ^{+) / 2, (9 +} tanθ-t - characterized in that it is set) / 2, (13-cotθ + t +) / 2, and ^{(15 + tanθ + t +)} / 2 -) / 2, (11-cotθ-t Any one of claims 2 to 4 The described distance measuring device.

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