Imaging device

Abstract

To better reduce the effect of a dark current in an imaging apparatus.SOLUTION: An imaging apparatus (200) includes a pixel array having a plurality of imaging elements arranged according to a predetermined pattern, a correction value calculation circuit (102) that (i) determines a temperature-based correction value (HT) on the basis of the temperature (T) of the imaging element measured by a temperature sensor (101), (ii) determines a coordinate-based correction value (for example, HX) on the basis of the coordinates (for example, X) indicating the position of the imaging element within the pixel array, and (iii) determines a final correction value (H) on the basis of the temperature-based correction value and the coordinate-based correction value, and a correction circuit (103) that corrects the output value (Pout) of the imaging element in the pixel array on the basis of the final correction value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] One aspect of the present invention relates to an imaging device. [Background technology]

[0002] An imaging element (photoelectric conversion element) in an imaging device generates a current (photocurrent) according to the amount of light it receives. In the imaging device, the photocurrent is converted into a voltage, and the voltage is then AD (Analog / Digital) converted to determine the output value of the imaging device.

[0003] However, even when the image sensor itself is not receiving light, it generates a minute current (dark current). Therefore, the output value of the image sensor is affected by the dark current. Therefore, various methods have been proposed to reduce the effect of the dark current.

[0004] For example, Patent Document 1 discloses a technique for correcting an optical black (OB) step that occurs in an imaging device due to dark current without adding any additional components (e.g., sensors). Specifically, the imaging device of Patent Document 1 corrects the OB step using a predetermined correction table. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-68056 Summary of the Invention [Problem to be solved by the invention]

[0006] However, as will be described later, there is still room for improvement in specific techniques for reducing the influence of dark current. One aspect of the present invention aims to more appropriately reduce the influence of dark current in an imaging device than in the past. [Means for solving the problem]

[0007] In order to solve the above problem, an imaging device according to one aspect of the present invention includes a pixel array having a plurality of imaging elements arranged according to a predetermined pattern; a correction value calculation circuit that (i) determines a temperature-based correction value based on the temperature of the imaging elements measured by a temperature sensor, (ii) determines a coordinate-based correction value based on coordinates indicating a position of the imaging elements in the pixel array, and (iii) determines a final correction value based on the temperature-based correction value and the coordinate-based correction value; and a correction circuit that corrects output values ​​of the imaging elements in the pixel array based on the final correction value. the correction value calculation circuit determines the temperature-based correction value in accordance with a first polynomial that indicates a relationship between the temperature and the temperature-based correction value, and determines the coordinate-based correction value in accordance with a second polynomial that indicates a relationship between the coordinate and the coordinate-based correction value; the correction value calculation circuit includes a temperature-based correction value calculation circuit that determines the temperature-based correction value in accordance with the first polynomial, and a coordinate-based correction value calculation circuit that determines the coordinate-based correction value in accordance with the second polynomial, wherein the degree of the first polynomial is equal to the degree of the second polynomial; the temperature-based correction value calculation circuit and the coordinate-based correction value calculation circuit are a common calculation circuit, and the common calculation circuit determines the temperature-based correction value in accordance with the first polynomial in a first period, and determines the coordinate-based correction value in accordance with the second polynomial in a second period that does not overlap with the first period. [Effects of the Invention]

[0008] According to one aspect of the present invention, it is possible to more appropriately reduce the influence of dark current in an imaging device than ever before. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a diagram schematically illustrating the configuration of a control circuit in the imaging device of the first embodiment. [Figure 2] 1 is a diagram schematically illustrating the configuration of an imaging device according to a first embodiment. [Figure 3] 10 is a graph illustrating the distribution of output values ​​in the X direction in a comparative example. [Figure 4] FIG. 2 is a diagram illustrating an example of the configuration of a temperature-based correction value calculation circuit according to the first embodiment. [Figure 5] 10 is a graph showing an example of known data showing the relationship between temperature and output value. [Figure 6] FIG. 2 is a diagram illustrating an example of the configuration of a coordinate-based correction value calculation circuit according to the first embodiment. [Figure 7] FIG. 10 is a diagram illustrating an example of operation timing of a correction value calculation circuit. [Figure 8] 10 is a graph illustrating the distribution of corrected output values ​​in the X direction in an example. [Figure 9]FIG. 10 is a diagram schematically illustrating the configuration of a control circuit in an imaging device according to a second embodiment. [Figure 10] FIG. 10 is a diagram illustrating an example of the configuration of a coordinate-based correction value calculation circuit according to the second embodiment. [Figure 11] FIG. 10 is a diagram schematically illustrating the configuration of a control circuit in an imaging device according to a third embodiment. [Figure 12] FIG. 10 is a diagram illustrating an example of the configuration of a common arithmetic circuit according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Embodiment 1] The imaging device 200 of the first embodiment will be described below. For convenience of explanation, components (structural elements) having the same functions as those described in the first embodiment will be denoted by the same reference numerals, and the description thereof will not be repeated in the following embodiments. For simplicity, the description of matters similar to those in the known art will also be omitted as appropriate.

[0011] It should be noted that the components and numerical values ​​described in this specification are merely examples unless otherwise specified. Therefore, unless otherwise specified, the positional relationship and number of components are not limited to the examples in each drawing. It should also be noted that each drawing is intended to schematically illustrate the shape, structure, and positional relationship of each component, and is not necessarily drawn exactly as in reality.

[0012] (Overview of the imaging device 200) 1 is a diagram schematically illustrating the configuration of a control circuit 100 in an imaging device 200. The control circuit 100 includes a temperature sensor 101, a correction value calculation circuit 102, and a correction circuit 103. The correction value calculation circuit 102 includes a temperature-based correction value calculation circuit 1021, a coordinate-based correction value calculation circuit 1022, and a final correction value calculation circuit 1029. The operation of each part of the control circuit 100 will be described later.

[0013] 2 is a diagram schematically illustrating the configuration of an imaging device 200. The imaging device 200 in the first embodiment is, for example, a CMOS (Complementary Metal Oxide Semiconductor) type imaging device. The imaging device 200 includes a pixel array 201, an OB unit 202, and peripheral circuits 203. In the example of FIG. 2, the imaging device 200 includes four peripheral circuits 203.

[0014] The pixel array 201 is disposed in the center of the imaging device 200. The pixel array 201 has a plurality of imaging elements 290. The imaging element 290 in the first embodiment is, for example, a CMOS image sensor. In the example of FIG. 2, the plurality of imaging elements 290 are disposed two-dimensionally within the pixel array 201. In the imaging device 200, the lateral direction (horizontal direction, X direction) and vertical direction (vertical direction, Y direction) of the pixel array 201 are defined in advance. In the pixel array 201, the plurality of imaging elements 290 are disposed along both the X direction and the Y direction. Thus, in the example of FIG. 1, the plurality of imaging elements 290 are disposed two-dimensionally within the pixel array 201.

[0015] However, as will be apparent to those skilled in the art, in one aspect of the present invention, the multiple imaging elements 290 may be arranged in a predetermined pattern within the pixel array 201. For example, the multiple imaging elements 290 may be arranged one-dimensionally within the pixel array 201. As an example, the multiple imaging elements 290 may be arranged within the pixel array 201 only along the X direction (or only along the Y direction).

[0016] In the imaging device 200, a position within the pixel array 201 (e.g., the position of the imaging element 290 within the pixel array 201) can be represented by predetermined coordinates. Therefore, for example, in the imaging device 200, (i) the horizontal position of the imaging element 290 within the pixel array 201 can be represented by an X coordinate, and (ii) the vertical position of the imaging element 290 within the pixel array 201 can be represented by a Y coordinate. Therefore, in the imaging device 200, the two-dimensional position of the imaging element 290 within the pixel array 201 can be represented by coordinates including an X coordinate and a Y coordinate (XY coordinates as two-dimensional coordinates). In addition, in the imaging device 200, the two-dimensional position within the imaging device 200 can also be represented by XY coordinates.

[0017] The OB section 202 is disposed on the outer periphery of the pixel array 201 so as to surround the pixel array 201. The OB section 202 has metal wiring as a light-shielding member. The imaging device 200 further includes an imaging element (not shown) within the OB section 202 that is shielded from light by the metal wiring (for convenience, referred to as a light-shielded imaging element). In the imaging device 200, the output value of the light-shielded imaging element is used as a reference value for the black level (BLEVEL).

[0018] The peripheral circuits 203 are arranged on the outer periphery of the OB section 202. The peripheral circuits 203 include various analog and digital circuits required for signal processing and control in the imaging device 200. For example, the peripheral circuits 203 include an AD conversion circuit and an image processing circuit. In the imaging device 200, the control circuit 100 only needs to be provided in at least one of the multiple peripheral circuits 203. In the example of FIG. 2, the control circuit 100 is provided in one of the four peripheral circuits 203.

[0019] (Problems with conventional imaging devices) Next, before describing the operation of the control circuit 100, problems with conventional imaging devices will be described. Below, an example of a conventional imaging device will be considered as a comparative example. Specifically, as an imaging device according to the comparative example, an imaging device in which the control circuit 100 has been removed from the imaging device 200 will be considered. Therefore, the positional relationship of each part of the imaging device according to the comparative example is the same as the example in FIG. 2.

[0020] As mentioned above, the output value of an imaging device is affected by dark current. In this specification, the output value of an imaging device refers to the output value of the imaging element (including the light-shielded imaging element) included in the imaging device. It is also known that the higher the temperature of the imaging device, the larger the dark current. For example, it is empirically known that the dark current increases approximately twofold for every 8 to 10°C rise in the temperature of the imaging device. The minimum output value of an imaging device is determined by identifying noise caused by dark current, etc. Therefore, in order to minimize the minimum output value of an imaging device, it is necessary to reduce or eliminate the dark current as much as possible.

[0021] One known method for reducing dark current is to perform hydrogen sintering during the manufacturing process of an image sensor. Hydrogen sintering is a manufacturing process in which heat treatment is performed in an atmosphere containing hydrogen. Hydrogen sintering deactivates impurity levels that cause dark current.

[0022] FIG. 3 is a graph illustrating the distribution of the above-mentioned output value (Pout) in the X direction in a comparative example. FIG. 3 is a diagram for explaining the influence of dark current on the output value. The unit of Pout in the graph in FIG. 3 is LSB (Least Significant Bit). In the comparative example, it is assumed that the coordinates of the bottom left position of the OB section 202 are set to (X, Y) = (0, 0). X = 0 corresponds to the left end of the OB section 202. On the other hand, X = 8000 (the right end of the graph in FIG. 3) corresponds to the right end of the OB section 202. The example in FIG. 3 shows the correspondence relationship between X and Pout at a certain Y position within the pixel array 201.

[0023] As can be seen from FIG. 3, the output value is particularly small near X=4000 (the center of pixel array 201). In contrast, the output value increases as one moves away from the center. For example, the output value is particularly large near X=0 and 8000. In this way, the inventor of the present application (hereinafter simply referred to as the "inventor") has confirmed that "the output value tends to increase from the center of pixel array 201 toward the periphery of pixel array 201" (for convenience, this will be referred to as "the output value non-uniformity tendency").

[0024] One of the reasons for the tendency for output values ​​to be non-uniform is thought to be that "in the OB section 202, the effectiveness of the above-mentioned hydrogen sintering process is less pronounced than in the pixel array 201 due to the shading of the image sensor by the metal wiring."

[0025] As described above, dark current has a high temperature dependency. The temperature of an imaging device is affected by external factors such as air temperature. In addition, the imaging device generates heat due to its operation. Therefore, the temperature of the imaging device is also affected by the self-heating.

[0026] From this, another possible reason for the tendency for output values ​​to be non-uniform is that "the operation of the peripheral circuit 203 causes the peripheral part of the pixel array 201 to be hotter than the central part of the pixel array 201."

[0027] Furthermore, the majority of the total heat dissipation from an imaging device occurs from the package terminals of the imaging element (e.g., CMOS image sensor) to the printed circuit board. On the other hand, it is estimated that approximately 10 to 20 percent of the total heat dissipation occurs from the chip surface of the imaging element. For this reason, the tendency toward non-uniform output values ​​shown in Figure 3 is thought to be caused by the interaction of three factors: the effectiveness of the hydrogen sintering process, heat generation, and heat dissipation.

[0028] Incidentally, the inventor set a light-shielded state in a high-temperature environment as the imaging conditions when acquiring the graph of FIG. 3. The inventor also set the black level of the imaging device to 128. That is, the inventor set BLEVEL=128. Therefore, according to the above imaging conditions, ideally, it is expected that the output value will be 128 at any position in the X direction.

[0029] However, as shown in Fig. 3, in the actual shooting results, the output value was lower than 128 in the center of the pixel array 201. This is because in the comparative example (conventional imaging device), a subtraction process is performed to match the output value in the OB section 202 to the black level (128). In the comparative example, the output value in the OB section 202 before the subtraction process was 138. Therefore, the graph in Fig. 3 is obtained as a result of a subtraction process in which each output value before the subtraction process is uniformly (evenly) subtracted by 10.

[0030] As described above, in the comparative example, even though the output values ​​in the central portion of pixel array 201 are smaller than the output values ​​in OB portion 202 before the subtraction process, the output values ​​in the central portion of pixel array 201 are also uniformly subtracted by 10. For this reason, as shown in FIG. 3 , an output value lower than the black level is obtained in the central portion of pixel array 201.

[0031] As described above, the uniform subtraction process in the conventional imaging device has a problem in that it is not possible to properly remove the influence of dark current. This problem in the conventional imaging device is caused by the output value correction process (uniform subtraction process) that does not take into account the tendency of output value non-uniformity.

[0032] (Configuration example of control circuit 100) The inventors have created an imaging device 200 (particularly a control circuit 100) to solve the above-mentioned problems of conventional imaging devices. As described below, the control circuit 100 makes it possible to correct the output value of an imaging element in accordance with the temperature and position of the imaging element. In this specification, the output values ​​of the multiple imaging elements 290 in the pixel array 201 are also collectively referred to as "output values ​​of the pixel array 201." The output values ​​of the pixel array 201 are part of the above-mentioned Pout.

[0033] (Temperature Sensor 101) The temperature sensor 101 measures the temperature (T) of the image sensor 290. As an example, the temperature sensor 101 may be formed inside the image sensor 200 (inside the control circuit 100 in the example of FIG. 1) by a known CMOS standard process. For details about the CMOS standard process, see, for example, Japanese Patent Application Laid-Open No. 2014-153156.

[0034] It should be noted that the temperature sensor 101 does not necessarily have to have high accuracy. This is because it is sufficient to obtain data indicating the relationship between T and the output ratio (see, for example, FIG. 4, which will be described later) through the measurement results of the temperature sensor 101. This data can also be said to be data that indirectly indicates the relationship between the dark current and the temperature.

[0035] (Correction value calculation circuit 102) In the correction value calculation circuit 102, the temperature-based correction value calculation circuit 1021 acquires T from the temperature sensor 101. The coordinate-based correction value calculation circuit 1022 acquires the above-mentioned coordinates (more precisely, coordinate data) from the pixel array 201. In this way, the correction value calculation circuit 102 acquires T and the coordinates.

[0036] (Temperature-based correction value calculation circuit 1021) Fig. 4 is a diagram showing an example of the configuration of the temperature-based correction value calculation circuit 1021. The temperature-based correction value calculation circuit 1021 includes multipliers 10211 to 10213 and an adder 10214. In the example of Fig. 4, the multipliers are denoted as "MULT" and the adder is denoted as "ADD." Also, as shown in Fig. 4, the symbol "*" in this specification is an operator representing a product.

[0037] The temperature-based correction value calculation circuit 1021 determines the temperature-based correction value (HT) according to a polynomial (for convenience, referred to as a "first polynomial") that indicates the relationship between T and the temperature-based correction value (HT). In the example of the first embodiment, the first polynomial is HT=A1*T 2 +A2*T+A3 …(1) In equation (1), A1 to A3 are coefficients for fitting (more specifically, polynomial fitting).

[0038] A1 to A3 may be stored in a memory (not shown) of the imaging device 200. Alternatively, A1 to A3 may be written in advance in the control circuit 100. A method for determining A1 to A3 will be described later. These matters regarding A1 to A3 also apply similarly to other coefficients for fitting, which will be described later.

[0039] As described above, the first polynomial in the first embodiment is a quadratic polynomial expressed as shown in Equation (1). The temperature-based correction value calculation circuit 1021 in FIG. 4 is configured to execute a temperature-based correction value determination calculation (a calculation to determine a temperature-based correction value) according to Equation (1). However, as will be apparent to those skilled in the art, the configuration of the temperature-based correction value calculation circuit 1021 is not limited to the example in FIG. 4. The same applies to the coordinate-based correction value calculation circuit 1022 described later.

[0040] 4, in the temperature-based correction value calculation circuit 1021, A2 and T are input to two input terminals of a multiplier 10211. Therefore, A2*T is output from the output terminal of the multiplier 10211.

[0041] The multiplier 10212 is located at the same stage as the multiplier 10211. T is input to two input sections of the multiplier 10212. Therefore, T is output from the output section of the multiplier 10212. 2 will be output.

[0042] The multiplier 10213 is located after the multiplier 10212. One of the two inputs of the multiplier 10213 receives the output of the multiplier 10212, i.e., T 2 is input to the other of the two inputs of the multiplier 10213. Therefore, A1*T is output from the output of the multiplier 10213. 2 will be output.

[0043] The adder 10214 is located at the final stage of the temperature-based correction value calculation circuit 1021. The adder 10214 has three inputs: (i) A2*T (the output of the multiplier 10211), (ii) A1*T 2 (the output of the multiplier 10213), and (iii) A3 are input. Therefore, the value of the right-hand side of equation (1) (in other words, HT) is output from the output section of the adder 10214.

[0044] As an example, A1 to A3 in formula (1) may be set based on known data showing the relationship between T and Pout. FIG. 5 is a graph showing an example of known data showing the relationship between T and Pout, obtained through a prior experiment by the inventor. The horizontal axis in the graph of FIG. 5 represents temperature (T). The vertical axis in the graph of FIG. 5 represents the output ratio. In this specification, the output ratio (PR) is defined as PR=Pout(T) / Pout(T0) Pout(T) represents Pout at temperature T. T0 is a reference temperature (e.g., room temperature). In the example of FIG. 5, T0=30°C.

[0045] In the example of Fig. 5, as T increases from T0, Pout increases approximately quadratically. Therefore, for example, A1 to A3 may be determined so as to fit a quadratic function to the graph plot of Fig. 5. In the example of the first embodiment, A1=4.060*10 -5 ; A2=-3.160*10 -3 ; A3=1.0601; A1 to A3 are determined as follows.

[0046] According to the first embodiment, HT can be determined by a simple polynomial, for example, equation (1). Therefore, the temperature-based correction value calculation circuit 1021 can be realized with a simple circuit configuration.

[0047] (Coordinate-based correction value calculation circuit 1022) Fig. 6 is a diagram showing an example of the configuration of the coordinate-based correction value calculation circuit 1022. The coordinate-based correction value calculation circuit 1022 includes multipliers 10221 to 10223 and an adder 10224. As is clear from Fig. 6, the circuit configuration of the coordinate-based correction value calculation circuit 1022 is similar to that of the temperature-based correction value calculation circuit 1021 (see Fig. 4 above).

[0048] The coordinate-based correction value calculation circuit 1022 determines the coordinate-based correction value according to a polynomial (for convenience, referred to as a "second polynomial") that indicates the relationship between the coordinate and the coordinate-based correction value. In the first embodiment, the second polynomial is a polynomial that indicates the relationship between the X coordinate and the coordinate-based correction value. Therefore, the coordinate-based correction value in the following description will be represented as HX.

[0049] In the example of embodiment 1, the second polynomial is HX=B1*X 2 +B2*X+B3 …(2) In equation (2), B1 to B3 are coefficients for fitting. Thus, in the example of embodiment 1, the second polynomial is a quadratic polynomial expressed as equation (2). The coordinate-based correction value calculation circuit 1022 in FIG. 6 is configured to execute a coordinate-based correction value determination calculation (a calculation to determine a coordinate-based correction value) according to equation (2).

[0050] 6, in the coordinate-based correction value calculation circuit 1022, B2 and X are input to two input portions of a multiplier 10221. Therefore, B2*X is output from the output portion of the multiplier 10221.

[0051] The multiplier 10222 is located at the same stage as the multiplier 10221. X is input to each of the two input sections of the multiplier 10222. Therefore, X is output from the output section of the multiplier 10222. 2 will be output.

[0052] The multiplier 10223 is located after the multiplier 10222. One of the two inputs of the multiplier 10223 receives the output of the multiplier 10222, i.e., X 2 is input to the other of the two inputs of the multiplier 10223. Therefore, the output of the multiplier 10223 is B1*X 2 will be output.

[0053] The adder 10224 is located at the final stage of the coordinate-based correction value calculation circuit 1022. The adder 10224 receives (i) B2*X (the output of the multiplier 10221), (ii) B1*X 2 (the output of the multiplier 10223), and (iii) B3 are input. Therefore, the output of the adder 10224 outputs the value of the right-hand side of equation (2) (in other words, HX).

[0054] As an example, B1 to B3 in equation (2) may be set based on known data showing the relationship between X and Pout. Pout in the example of FIG. 3 above can be approximately considered to be a quadratic function of X. Therefore, B1 to B3 may be determined so as to fit a quadratic function to the graph plot of FIG. 3, for example. In the example of embodiment 1, B1=5.284*10 -7 ; B2=-4.121*10 -3 ; B3=125.8; As a result, B1 to B3 are determined.

[0055] According to the example of the first embodiment, HX can be determined by a simple polynomial, for example, equation (2). Therefore, the coordinate-based correction value calculation circuit 1022 can be realized by a simple circuit configuration.

[0056] (Another example of a second polynomial) As will be apparent to those skilled in the art, the second polynomial is not limited to a quadratic polynomial. That is, the degree of the second polynomial is not limited to 2. In order to correct the output value in the control circuit 100 with higher precision, the degree of the second polynomial may be set to be greater than 2. Note that, as will be apparent to those skilled in the art, the following description of other examples of the second polynomial also applies to the first polynomial.

[0057] As an example, the degree of the second polynomial may be set to 6. In this case, the second polynomial is HX=B1*X 6 +B2*X 5 +B3*X 4 +B4*X 3 +B5*X 2 +B6*X+B7 …(3) In this case, the coordinate-based correction value calculation circuit 1022 may be configured to execute the coordinate-based correction value determination calculation according to equation (3).

[0058] As an example, B1 to B7 may be determined by fitting a sextic function to the graph plot in FIG. B1=7.473*10- 21 ; B2=-1,749*10 -16 ; B3=1.576*10 -12 ; B4=-6.846*10 -9 ; B5=1.501*10 -5 ; B6=-1.677*10 -2 ; B7=128.03; As a result, B1 to B7 may be determined.

[0059] (Final correction value calculation circuit 1029) The final correction value calculation circuit 1029 (i) acquires a temperature-based correction value (HT) from the temperature-based correction value calculation circuit 1021, and (ii) acquires a coordinate-based correction value (HX) from the coordinate-based correction value calculation circuit 1022. The final correction value calculation circuit 1029 determines a final correction value (H) based on HT and HT. In this specification, the calculation to determine the final correction value is referred to as a final correction value determination calculation.

[0060] As an example, the final correction value calculation circuit 1029 may derive the product of HT and HT as H. That is, the final correction value calculation circuit 1029 may calculate H=HT*HX …(4) HT and H depending on HT may be determined according to:

[0061] According to the example of the first embodiment, H can be determined by the simple calculation formula, formula (4). Therefore, the final correction value calculation circuit 1029 can be realized by a simple circuit configuration (e.g., a multiplier). However, as will be clear to those skilled in the art, the formula for deriving H is not limited to formula (4).

[0062] (correction circuit 103) The correction circuit 103 (i) acquires an output value (Pout) from the pixel array 201, and (ii) acquires a final correction value (H) from the correction value calculation circuit 102 (more specifically, the final correction value calculation circuit 1029). The correction circuit 103 corrects Pout based on H. Specifically, the correction circuit 103 determines a corrected output value (Pout_H) according to H. Then, the correction circuit 103 outputs Pout_H.

[0063] As an example, the correction circuit 103 may determine Pout_H by subtracting H from Pout. In this way, the correction circuit 103 in the first embodiment may be a subtraction circuit. For example, the correction circuit 103 in the first embodiment may determine Pout_H by subtracting H from Pout. Pout_H=Pout-H+BLEVEL …(5) Pout_H may be determined according to the following formula:

[0064] According to equation (5), the output value can be corrected so that it is canceled by subtracting the final correction value. Therefore, the influence of dark current can be effectively reduced. However, as will be apparent to those skilled in the art, the calculation formula for Pout_H is not limited to equation (5).

[0065] (An example of the operation timing of the correction value calculation circuit 102) FIG. 7 is a diagram showing an example of the operation timing of the correction value calculation circuit 102. As shown in FIG. 7, temperature input (acquisition of T, which is the output value of the temperature sensor 101) is executed before acquisition of Pout (reading of the output value of the pixel array 201) is started. In the imaging device 200, it is preferable to determine H T using the same value of T until imaging of one image is completed (until output of the number of output values ​​corresponding to one image is completed). For this reason, in the example of FIG. 7, the value of T that was initially acquired is latched. As shown in FIG. 7, the temperature-based correction value determination calculation is executed in synchronization with the temperature input.

[0066] The imaging device 200 outputs images at a predetermined frame rate (e.g., 60 frames / second). However, the temperature sensor 101 does not necessarily need to measure T every frame. Therefore, for example, the temperature sensor 101 may measure T once every several frames. In this case, the power consumption caused by the operation of the temperature sensor 101 is reduced. Therefore, the power consumption of the imaging device 200 can be reduced.

[0067] 7, the coordinate input (acquisition of coordinates of the pixel array 201) corresponds to reading an address in the X direction of the pixel array 201. As shown in FIG. 7, the coordinate-based correction value determination calculation is executed in synchronization with the coordinate input. As a result, the final correction value determination calculation is also executed in synchronization with the coordinate input.

[0068] (Example) FIG. 8 is a graph illustrating the distribution of Pout_H in the X direction in an example. In FIG. 8, Pout is also plotted for comparison with Pout_H. The distribution of Pout in FIG. 8 is the same as the example in FIG. 3. Pout_H in FIG. 8 is determined according to the above-mentioned formula (6). Note that in the example in FIG. 8, HX is determined according to the above-mentioned formula (3) in order to correct Pout with higher accuracy.

[0069] As shown in Fig. 8, it was confirmed that Pout_H was equal to 128 (BLEVEL) for all Xs. In other words, in the example of Fig. 8, it was confirmed that Pout was corrected so that Pout was offset by subtracting H for all Xs. As described above, in the example of Fig. 8, H corresponding to X is determined so that H = Pout for all Xs.

[0070] (effect) As described above, according to the imaging device 200 (particularly, the control circuit 100), the correction value calculation circuit 102 can (i) determine a temperature-based correction value (HT) based on the temperature (T) of the imaging element 290 measured by the temperature sensor 101, and (ii) determine a coordinate-based correction value (HX) based on a coordinate (e.g., X) indicating the position of the imaging element 290 within the pixel array 201. Then, the correction value calculation circuit 102 can determine a final correction value (H) based on HT and HX. Next, the correction circuit 103 can correct the output value (Pout) of the imaging element 290 within the pixel array 201 based on H.

[0071] According to the above configuration, unlike the comparative example, the final correction value can be determined after taking into consideration the tendency of non-uniform output values. Then, by correcting the output value based on the final correction value, it becomes possible to correct the output value according to the coordinates (i.e., according to the position of the image sensor within the pixel array 201). Therefore, the influence of dark current can be reduced more appropriately than in the comparative example (conventional image pickup device).

[0072] [Embodiment 2] 9 is a diagram schematically illustrating the configuration of a control circuit 100V in an imaging device 200V according to the second embodiment. The correction value calculation circuit of the control circuit 100V is referred to as a correction value calculation circuit 102V. The correction value calculation circuit 102V includes a coordinate-based correction value calculation circuit 1023 instead of the coordinate-based correction value calculation circuit 1022. As described below, the coordinate-based correction value calculation circuit 1023 is a modified version of the coordinate-based correction value calculation circuit 1022.

[0073] 10 is a diagram showing an example of the configuration of the coordinate-based correction value calculation circuit 1023. The coordinate-based correction value calculation circuit 1023 includes a multiplexer 10231, a multiplier 10232, three FFs (Flip Flops) 10233, and an adder 10234. In the example of FIG. 10, the multiplexer 10231 is denoted as "MUX." The three FFs 10233 are also referred to as FF10233a, FF10233b, and FF10233c. FF10233a, FF10233b, and FF10233c may also be referred to as the first FF, the second FF, and the third FF, respectively.

[0074] The multiplexer 10231 has four inputs and two outputs. 2 (Output of FF10233a), B1, B2 and X are input.

[0075] The multiplexer 10231 selects four input signals (X 2 , B1, B2, and X) are selected as output signals. Of the two output sections of the multiplexer 10231, in_a (first output signal) is output from one output section, and in_b (second output signal) is output from the other output section. Therefore, in_a is equal to one of the above four input signals. Also, in_b is equal to one of three signals obtained by excluding the signal corresponding to in_a from the above four input signals. In one example, in_a is equal to B2, and in_b is equal to X.

[0076] The multiplier 10232 is located after the multiplexer 10231. in_a and in_b are input to two input sections of the multiplier 10232. Therefore, in_a*in_b is output from the output section of the multiplier 10232.

[0077] The three FFs 10233 are located after the multiplier 10232. Each of the three FFs 10233 holds the output (in_a*in_b) of the multiplier 10222 for a certain period of time. Each of the three FFs 10233 holds a different in_a*in_b value.

[0078] In the example of Figure 10, FF10233a is a value of in_a*in_b, 2 FF10233a holds the value it holds (X 2 ) to the multiplexer 10231. FF10233b holds B2*X as another value of in_a*in_b. FF10233b supplies the value (B2*X) it holds to the adder 10234. FF10233c holds B1*X as yet another value of in_a*in_b. 2 FF10233c holds the value it holds (B1*X 2 ) is supplied to adder 10234.

[0079] The adder 10234 is located at the final stage of the coordinate-based correction value calculation circuit 1023. The adder 10234 receives (i) B2*X (output of FF10233b), (ii) B1*X 2 (iii) B3 (output of FF10233c) and (iii) B4 are input. Therefore, the value of the right side of the above equation (2) (in other words, HX) is output from the output part of the adder 10234. In this way, the calculation according to equation (2) can also be performed by using the coordinate-based correction value calculation circuit 1023 instead of the coordinate-based correction value calculation circuit 1022.

[0080] Generally, a multiplier has a larger circuit area than an adder. Therefore, in order to reduce the size of a coordinate-based correction value calculation circuit, it is preferable to reduce the number of multipliers included in the coordinate-based correction value calculation circuit as much as possible. Based on this idea, the inventor created the coordinate-based correction value calculation circuit 1023. As is clear from FIG. 10 , the coordinate-based correction value calculation circuit 1023 can be realized with fewer multipliers (e.g., one multiplier) than the coordinate-based correction value calculation circuit 1022 (see FIG. 6 above) by using a multiplexer and a flip-flop. In this way, the coordinate-based correction value calculation circuit 1023 can achieve a smaller size of the coordinate-based correction value calculation circuit.

[0081] As will be apparent to those skilled in the art, the temperature-based correction value calculation circuit 1021 in Figure 4 can also be replaced with a circuit configuration similar to that in Figure 10. Therefore, according to one aspect of the present invention, it is also possible to reduce the size of the temperature-based correction value calculation circuit. As described above, according to one aspect of the present invention, the use of a multiplexer and FFs makes it possible to reduce the size of the correction value calculation circuit.

[0082] [Embodiment 3] In the above-described embodiments, the temperature-based correction value calculation circuit and the coordinate-based correction value calculation circuit are separate calculation circuits. However, as described below, the temperature-based correction value calculation circuit and the coordinate-based correction value calculation circuit can also be a common circuit.

[0083] 11 is a diagram schematically illustrating the configuration of a control circuit 100W in an imaging device 200W according to Embodiment 3. The correction value calculation circuit of the control circuit 100W is referred to as a correction value calculation circuit 102W. The correction value calculation circuit 102W includes a common calculation circuit 1024 (common calculation circuit) instead of a temperature-based correction value calculation circuit (e.g., temperature-based correction value calculation circuit 1021) and a coordinate-based correction value calculation circuit (coordinate-based correction value calculation circuit 1022).

[0084] Fig. 12 is a diagram showing an example of the configuration of the common arithmetic circuit 1024. Note that the symbol " / " in Fig. 12 means "or." The common arithmetic circuit 1024 includes multipliers 10241 to 10243 and an adder 10244. As is clear from Fig. 12, the circuit configuration of the common arithmetic circuit 1024 is similar to that of the temperature-based correction value calculation circuit 1021 and the coordinate-based correction value calculation circuit 1022 (see also Figs. 4 and 5 above).

[0085] 12, during a period for the temperature-based correction value determination calculation (for convenience, referred to as the "first period"), T and A1 to A3 are supplied to the common calculation circuit 1024. During the first period, the common calculation circuit 1024 outputs HT by performing the same operation as the temperature-based correction value calculation circuit 1021 described above.

[0086] Furthermore, during a period for coordinate-based correction value determination calculation (for convenience, referred to as a "second period"), X and B1 to B3 are supplied to the common calculation circuit 1024. In the example of FIG. 12, the second period does not overlap with the first period. During the second period, the common calculation circuit 1024 outputs HX by performing the same operation as the coordinate-based correction value calculation circuit 1022 described above.

[0087] As is clear from the above description of the first embodiment, when the degree of the first polynomial is equal to the degree of the second polynomial, the configuration of the coordinate-based correction value calculation circuit is the same as the configuration of the temperature-based correction value calculation circuit. Therefore, when the degree of the first polynomial is equal to the degree of the second polynomial, it is possible to share the coordinate-based correction value calculation circuit and the temperature-based correction value calculation circuit, as shown in Fig. 12. The common calculation circuit 1024 can reduce the circuit area of ​​the correction value calculation circuit, thereby realizing miniaturization of the correction value calculation circuit.

[0088] As will be apparent to those skilled in the art, the common arithmetic circuit 1024 in Fig. 12 can be replaced with a circuit configuration similar to that shown in Fig. 10. In this case, the correction value arithmetic circuit can be further miniaturized.

[0089] (Supplementary information on the third embodiment) When the temperature-based correction value calculation circuit and the coordinate-based correction value calculation circuit are separate calculation circuits, the first period and the second period can overlap (see, for example, the above-mentioned first embodiment). That is, when the temperature-based correction value calculation circuit and the coordinate-based correction value calculation circuit are separate calculation circuits, the temperature-based correction value determination calculation and the coordinate-based correction value determination calculation can be executed in parallel (for example, simultaneously).

[0090] Therefore, whether the temperature-based correction value calculation circuit and the coordinate-based correction value calculation circuit are separate or common may be decided appropriately by the designer of the imaging device, for example, depending on the manufacturing specifications of the imaging device.

[0091] [Modification] In the above-described embodiments, the correction value calculation circuit determines the coordinate-based correction value (HX) based on the X coordinate (X). However, the correction value calculation circuit according to one aspect of the present invention may determine the coordinate-based correction value based on at least one of the X coordinate and the Y coordinate.

[0092] As an example, the correction value calculation circuit may determine a coordinate-based correction value (HY) based on the Y coordinate (Y). In this case, for example, the correction value calculation circuit may use the following equation: HY=C1*Y 2 +C2*Y+C3 …(6) HY may be determined according to Y according to the following formula. C1 to C3 in formula (6) are coefficients for fitting. Formula (6) is another example of a second polynomial.

[0093] For example, depending on the manufacturing specifications of the imaging device, it is possible that fluctuations in Pout occur more significantly in the Y direction than in the X direction. In such cases, in order to correct Pout with higher precision, it is preferable to determine the coordinate-based correction value based on the Y coordinate.

[0094] As another example, the correction value calculation circuit may determine a coordinate-based correction value (HXY) based on both the X coordinate (X) and the Y coordinate (Y). In this case, for example, the correction value calculation circuit may use the following equation: HXY=D1*X 2 +D2*X+D3 +E1*Y 2 +E2*Y+E3 …(7) HXY may be determined according to X and Y according to the following formula. D1 to D3 and E1 to E3 in formula (7) are coefficients for fitting. Formula (7) is yet another example of a second polynomial.

[0095] When multiple imaging elements are arranged two-dimensionally in a pixel array, it is more preferable to consider fluctuations in Pout in both the X and Y directions. Therefore, when multiple imaging elements are arranged two-dimensionally in a pixel array, it is more preferable to determine a coordinate-based correction value based on both the X and Y coordinates in order to correct Pout with higher accuracy.

[0096] [Modification] In the above-described embodiments, the imaging device has been illustrated as having a temperature sensor (e.g., temperature sensor 101) inside the imaging device. However, the imaging device according to an aspect of the present invention does not necessarily have to have a temperature sensor. For example, the temperature sensor according to an aspect of the present invention may be provided outside the imaging device. The temperature sensor only needs to be positioned so as to be able to measure the temperature (T) of the imaging element. In this case, the imaging device may acquire T from the temperature sensor via any communication interface.

[0097] However, if the temperature sensor and the imaging device are separated from each other, the temperature sensor measurement value T may include factors other than the self-heating of the imaging device, such as the self-heating of peripheral devices of the imaging device.

[0098] Therefore, in order to correct Pout with high accuracy, it is preferable to arrange the temperature sensor so that the above-mentioned other factors are excluded from the measurement value of the temperature sensor. For this reason, it is preferable that the temperature sensor according to one aspect of the present invention is provided inside the imaging device. This can improve the validity of the measurement value of the temperature sensor.

[0099] As described in the first embodiment above, if a temperature sensor is provided inside the imaging device, the measurement value (T) of the temperature sensor acquired once may be latched so that it does not change during the readout period of Pout (the acquisition period of Pout).

[0100] Furthermore, as described in the first embodiment above, when a temperature sensor is provided inside the imaging device, the measurement of T by the temperature sensor may be performed for each frame, or may be performed once for multiple frames.

[0101] Furthermore, if a temperature sensor is provided inside the imaging device, the temperature sensor may output a statistical value (e.g., average or median) of T measured multiple times. In this case, the correction value calculation circuit may determine the temperature-based correction value based on the statistical value of T.

[0102] [Software implementation example] The functions of the imaging devices 200 to 200V (hereinafter referred to as "devices") can be realized by a program that causes a computer to function as the devices, and a program that causes a computer to function as each control block of the devices (particularly each part included in the control circuits 100 to 100V).

[0103] In this case, the device includes a computer having at least one control device (e.g., a processor) and at least one storage device (e.g., a memory) as hardware for executing the program. The control device and storage device execute the program, thereby realizing the functions described in each of the above embodiments.

[0104] The program may be non-transitory and may be recorded on one or more computer-readable recording media. The recording media may or may not be included in the device. In the latter case, the program may be supplied to the device via any wired or wireless transmission medium.

[0105] In addition, some or all of the functions of the control blocks can be realized by logic circuits. For example, an integrated circuit in which a logic circuit that functions as each of the control blocks is formed is also included in the scope of one aspect of the present invention. In addition, the functions of the control blocks can be realized by, for example, a quantum computer.

[0106] Furthermore, each process described in each of the above embodiments may be executed by AI (Artificial Intelligence). In this case, the AI ​​may run on the control device or on another device (for example, an edge computer or a cloud server).

[0107] 〔summary〕 An imaging device (e.g., 200) according to aspect 1 of the present invention includes a pixel array (201) having a plurality of imaging elements (290) arranged according to a predetermined pattern, a correction value calculation circuit (e.g., 102) that (i) determines a temperature-based correction value based on the temperature (T) of the imaging element measured by a temperature sensor (101), (ii) determines a coordinate-based correction value (e.g., HX) based on a coordinate (e.g., X) indicating the position of the imaging element within the pixel array, and (iii) determines a final correction value (H) based on the temperature-based correction value and the coordinate-based correction value, and a correction circuit (103) that corrects an output value (Pout) of the imaging element within the pixel array based on the final correction value.

[0108] According to the above configuration, the final correction value can be determined based on the temperature-based correction value determined according to the temperature and the coordinate-based correction value determined according to the coordinate. That is, the final correction value can be determined taking into account the above-mentioned tendency toward uneven output values. Next, by correcting the output value based on the final correction value, it becomes possible to correct the output value according to the position of the image sensor within the pixel array. Therefore, the influence of dark current can be reduced more effectively than before.

[0109] In the imaging device according to Aspect 2 of the present invention, in Aspect 1, the correction circuit may be a subtraction circuit that determines a corrected output value (Pout_H) by subtracting the final correction value from the output value.

[0110] According to the above configuration, the output value can be corrected by subtracting the final correction value so as to cancel out the output value, thereby effectively reducing the influence of dark current.

[0111] In the imaging device according to a third aspect of the present invention, in the first or second aspect, the correction value calculation circuit may derive the product of the temperature-based correction value and the coordinate-based correction value as the final correction value.

[0112] According to the above configuration, the final correction value can be determined by a simple calculation formula, for example, the above formula (4), and therefore the configuration of the correction value calculation circuit can be simplified.

[0113] In an imaging device according to aspect 4 of the present invention, in any one of aspects 1 to 3, the correction value calculation circuit may determine the temperature-based correction value according to a first polynomial that indicates the relationship between the temperature and the temperature-based correction value, and may determine the coordinate-based correction value according to a second polynomial that indicates the relationship between the coordinate and the coordinate-based correction value.

[0114] According to the above configuration, the temperature-based correction value can be determined by a simple calculation formula, for example, the above formula (1).Similarly, the coordinate-based correction formula can be determined by a simple calculation formula, for example, the above formula (2).

[0115] In the imaging device according to aspect 5 of the present invention, in the above-mentioned aspect 4, the correction value calculation circuit includes a temperature-based correction value calculation circuit (1021) that determines the temperature-based correction value according to the first polynomial, and a coordinate-based correction value calculation circuit (e.g., 1022) that determines the coordinate-based correction value according to the second polynomial.

[0116] According to the above configuration, a temperature-based correction value calculation circuit can be realized with a simple circuit configuration.Similarly, a coordinate-based correction value calculation circuit can be realized with a simple circuit configuration.

[0117] In the imaging device according to a sixth aspect of the present invention, in the fifth aspect, the temperature-based correction value calculation circuit and the coordinate-based correction value calculation circuit may be separate calculation circuits.

[0118] According to the above configuration, the temperature-based correction value determination calculation and the coordinate-based correction value determination calculation can be executed in parallel.

[0119] In the imaging device according to aspect 7 of the present invention, in aspect 5, the degree of the first polynomial is equal to the degree of the second polynomial, and the temperature-based correction value calculation circuit and the coordinate-based correction value calculation circuit may be a common calculation circuit (e.g., common calculation circuit 1024).

[0120] According to the above configuration, by using a common circuit for the temperature-based correction value calculation circuit and the coordinate-based correction value calculation circuit, it is possible to reduce the size of the correction value calculation circuit.

[0121] In an imaging device according to aspect 8 of the present invention, in any one of aspects 1 to 7, the multiple imaging elements are arranged along both the horizontal and vertical directions within the pixel array, and the coordinates include (i) an X coordinate indicating the horizontal position of the imaging element within the pixel array, and (ii) a Y coordinate indicating the vertical position of the imaging element within the pixel array, and the correction value calculation circuit may determine the coordinate-based correction value based on at least one of the X coordinate and the Y coordinate.

[0122] According to the above configuration, the coordinate-based correction value can be determined based on at least one of the X coordinate and the Y coordinate. Note that, in order to correct the output value with higher accuracy, it is preferable to determine the coordinate-based correction value based on both the X coordinate and the Y coordinate.

[0123] The imaging device according to a ninth aspect of the present invention is any one of the first to eighth aspects, and may further include the temperature sensor inside the imaging device.

[0124] According to the above configuration, the validity of the measurement value (ie, T) of the temperature sensor can be improved.

[0125] [Additional Notes] One aspect of the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of one aspect of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. [Explanation of symbols]

[0126] 100, 100V, 100W control circuit 101 Temperature Sensor 102, 102V, 102W Correction value calculation circuit 103 Correction circuit (subtraction circuit) 200, 200V, 200W imaging device 201 pixel array 203 Peripheral Circuits 290 Image sensor 1021 Temperature base correction value calculation circuit 1022, 1023 Coordinate base correction value calculation circuit 1024 common arithmetic circuit (common arithmetic circuit) 1029 Final correction value calculation circuit T Temperature (temperature of the image sensor) X coordinate (the horizontal position of the image sensor within the pixel array) Y coordinate (the vertical position of the image sensor within the pixel array) HT Temperature-based correction value HX coordinate-based correction value (coordinate-based correction value determined based on the X coordinate) HY coordinate-based correction value (coordinate-based correction value determined based on the Y coordinate) HXY coordinate-based correction value (coordinate-based correction value determined based on the X and Y coordinates) H Final correction value Pout output value Pout_H Corrected output value

Claims

1. a pixel array having a plurality of imaging elements arranged according to a predetermined pattern; a correction value calculation circuit that (i) determines a temperature-based correction value based on the temperature of the image sensor measured by a temperature sensor, (ii) determines a coordinate-based correction value based on coordinates indicating the position of the image sensor within the pixel array, and (iii) determines a final correction value based on the temperature-based correction value and the coordinate-based correction value; a correction circuit that corrects an output value of the image sensor in the pixel array based on the final correction value, The correction value calculation circuit is determining the temperature-based correction value according to a first polynomial that describes a relationship between the temperature and the temperature-based correction value; determining the coordinate-based correction value according to a second polynomial relating the coordinates to the coordinate-based correction value; The correction value calculation circuit is a temperature-based correction value calculation circuit for determining the temperature-based correction value in accordance with the first polynomial; a coordinate-based correction value calculation circuit that determines the coordinate-based correction value in accordance with the second polynomial; the degree of the first polynomial is equal to the degree of the second polynomial; the temperature-based correction value calculation circuit and the coordinate-based correction value calculation circuit are a common calculation circuit, The common arithmetic circuit is determining the temperature-based correction value in accordance with the first polynomial during a first time period; determining the coordinate-based correction value in accordance with the second polynomial during a second time period that does not overlap with the first time period; Imaging device.

2. 2. The imaging device according to claim 1, wherein the correction circuit is a subtraction circuit that determines the corrected output value by subtracting the final correction value from the output value.

3. 3. The imaging device according to claim 1, wherein the correction value calculation circuit derives the final correction value as a product of the temperature-based correction value and the coordinate-based correction value.

4. the plurality of imaging elements are arranged along both the horizontal and vertical directions in the pixel array, the coordinates include (i) an X coordinate indicating the horizontal position of the imaging element within the pixel array, and (ii) a Y coordinate indicating the vertical position of the imaging element within the pixel array; 4. The imaging device according to claim 1, wherein the correction value calculation circuit determines the coordinate-based correction value based on at least one of the X coordinate and the Y coordinate.

5. The imaging device according to claim 1 , wherein the temperature sensor is disposed inside the imaging device.

Images