Photoelectric conversion device and photoelectric conversion system with photoelectric conversion device

Abstract

An exposure control unit, a timing generator unit, a metering unit, and a pulse control unit are provided. The exposure control unit generates a signal defining multiple second exposure periods contained within a first exposure period, which corresponds to a frame, each of which is shorter than the first exposure period. The timing generator unit generates a pulse signal defining the timing information within each second exposure period. The metering unit counts the pulse signal at or after the first photon capture in the second exposure period, based on the pulse signal generated by the timing generator unit. The pulse control unit performs pulse counting in a second exposure period following the first, based on a value from the metering unit.

Description

TECHNICAL AREA The present invention relates to photoelectric conversion devices and photoelectric conversion systems with photoelectric conversion devices. BACKGROUND OF THE INVENTION The international PCT publication WO 2020 / 179928 discloses a configuration that measures the time until a counter reaches saturation for each pixel and estimates the amount of light through an extrapolation method based on the measured time and the counter value. This configuration makes it possible to extend the dynamic range. According to the international PCT publication WO 2020 / 179928, signal information is missing after the counter stops due to saturation. This can lead to artifacts when imaging a moving object or to brightness fluctuations when imaging under a flickering light source. INVENTION SUMMARY A photoelectric conversion device comprises: a photoelectric conversion element configured to receive a photon; an exposure control device configured to generate a signal defining a plurality of second exposure periods contained within a first exposure period corresponding to a frame, each second exposure period being shorter than the first exposure period; a timing generator device configured to generate a pulse signal defining timing information within each second exposure period; and a measuring device configured to count the pulse signal at or after a first photon detection in the second exposure period based on the pulse signal generated by the timing generator device.and a pulse control device configured to perform a counting control of the pulse signal in a second exposure period following the second exposure period based on a value from the measuring device, wherein the subsequent second exposure period is one from the plurality of second exposure periods. Features of the present invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings. The following description of exemplary embodiments is based on examples. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 shows a configuration example of a pixel circuit. Figs. 2A and 2B show the relationship between a detection time and the number of incident photons. Figs. 3A to 3C show the relationship between the detection time and the number of incident photons. Figs. 4A to 4C show a photon detection probability. Figs. 5A to 5C show expected values ​​with respect to the number of incident photons and the input-output characteristic. Fig. 6 shows a photoelectric conversion device according to a first embodiment. Fig. 7 shows the photoelectric conversion device according to the first embodiment. Fig. 8 shows the photoelectric conversion device according to the first embodiment. Fig. 9 shows the photoelectric conversion device according to the first embodiment.Figures 10A to 10C show a pixel circuit of the photoelectric conversion device according to the first embodiment and its control. Figure 11 shows an operating sequence of the photoelectric conversion device according to the first embodiment. Figure 12 shows a case in which a clock signal defining time information has regular and irregular intervals. Figures 13A and 13B show the clock signal defining the time information and the input-output characteristic. Figures 14A and 14B show a pixel circuit of a photoelectric conversion device according to a second embodiment. Figure 15 shows an operating sequence of the photoelectric conversion device according to the second embodiment. Figure 16 shows a pixel circuit of a photoelectric conversion device according to a third embodiment.Figure 17 shows an operating sequence of the photoelectric conversion device according to the third embodiment. Figure 18 shows advantageous effects of the photoelectric conversion device according to the third embodiment. Figure 19 shows a photoelectric conversion device according to a fourth embodiment. Figure 20 shows a pixel circuit of the photoelectric conversion device according to the fourth embodiment. Figure 21 shows the signal processing blocks of a photoelectric conversion device according to a fifth embodiment. Figures 22A and 22B show schematic views according to a sixth embodiment. Figure 23 shows a functional block diagram of a photoelectric conversion system according to a seventh embodiment. Figures 24A and 24B show functional block diagrams of a photoelectric conversion system according to an eighth embodiment.Figure 25 shows a functional block diagram of a photoelectric conversion system according to a ninth embodiment. Figure 26 shows a functional block diagram of a photoelectric conversion system according to a tenth embodiment. Figures 27A and 27B show functional block diagrams of a photoelectric conversion system according to an eleventh embodiment. DETAILED DESCRIPTION OF THE EXECUTION EXAMPLES The embodiments described below are intended to illustrate the technical concept of the present invention and are not meant to limit it. The sizes and positional relationships of the elements shown in the drawings may sometimes be exaggerated for the sake of clarity. In the following description, identical components are designated with the same reference numerals, and their descriptions may sometimes be omitted. The following description may use terms that indicate specific directions and positions (e.g., "above," "below," "to the right," "to the left," and other terms encompassing these concepts). The use of these terms is intended to facilitate understanding of the exemplary embodiments with reference to the drawings and is not intended to limit the technical scope of the present invention. In this description, "top view" is a view from a direction perpendicular to the main surface of a semiconductor layer and is synonymous with "top view" or "view from above". Furthermore, "cross-sectional view" is a view from a direction perpendicular to a plane extending in the direction perpendicular to the main surface of the semiconductor layer. In the following description, the anode of a photodiode (PD) is set to a fixed potential, and a signal is extracted from the cathode. Therefore, a semiconductor region of the first conductivity type, where electric charges of the same polarity as the signal charge serve as the majority charge carriers, is an N-type semiconductor region, while a semiconductor region of the second conductivity type, where electric charges of opposite polarity to the signal charge serve as the majority charge carriers, is a P-type semiconductor region. Alternatively, the cathode of the PD can be set to a fixed potential, and a signal can be extracted from the anode.In this case, the semiconductor region of the first conductivity type, where electric charges of the same polarity as the signal charge serve as the majority charge carriers, is a P-type semiconductor region, while the semiconductor region of the second conductivity type, where electric charges of opposite polarity to the signal charge serve as the majority charge carriers, is an N-type semiconductor region. Although the following description refers to a case where one of the nodes of the PD is set to a fixed potential, the potentials of the two anodes can vary. Basic configuration Fig. 1 shows a schematic configuration of a photoelectric conversion device according to this embodiment. A photoelectric conversion device 100 comprises a photoelectric conversion element 1, an exposure control device 2, a timing generator device 3, a measuring device 4, and a pulse control device 5. The photoelectric conversion element 1 detects an incident photon and converts it into an electrical signal. The photoelectric conversion element 1 can be a linear-mode avalanche photodiode operated around its breakdown voltage, or a single-photon avalanche photodiode operated in Geiger mode. Exposure control unit 2 generates a signal that defines an exposure period (first exposure period) corresponding to a frame. An "exposure period corresponding to a frame" can also be referred to as a "frame period". Exposure control unit 2 also generates a signal that defines an exposure period (second exposure period) corresponding to each of several subframes contained within the exposure period corresponding to a frame. An "exposure period corresponding to a subframe" can also be referred to as a "subframe period". The timing generator device 3 generates a pulse signal to define time information within the subframe period (i.e., within the second exposure period). The measuring device 4 receives a signal from the photoelectric conversion element 1, a control signal from the exposure control device 2, and a control signal from the timing generator device 3 via the pulse control device 5. From these signals, the measuring device 4 measures a numerical value corresponding to the detection time of the first detected photon from the beginning of the subframe period. The measuring device 4 can be a general time-to-digital converter (TDC) circuit, which serves as the circuit that performs a time measurement, or it can perform the measurement based on another method. The pulse control unit 5 receives a signal from the measuring unit 4 and a signal from the timing generator unit 3. The pulse control unit 5 controls the number of control signals to be input into the measuring unit 4 based on the numerical value of the measuring unit 4. Fig. 2A shows the exposure period and the acquisition time, and Fig. 2B shows the relationship between the acquisition time and the number of incident photons. If the exposure period is defined as Tacc and the time from the start of the exposure period until a photon is detected as Tdetect, then the number Nph of incident photons arriving within the exposure period is expressed as: Nph = (Tacc / Tdetect). Thus, by determining the exposure period and the detection time, the number of incident photons can be estimated. In other words, since the number of incident photons can be determined without actually measuring the number of incident photons, a mapping is possible. Figures 3A and 3B show a case where the exposure shown in Figures 2A and 2B is repeated multiple times. In this case, one measurement period per exposure is called a "subframe period," and the subframe period is repeated N times. A frame period is the sum of the time from a first subframe to an Nth subframe. If, in this case, the average time that photons are detected in the subframes during a frame period is defined as Tave, then the number Nph of incident photons in a frame can be estimated as follows: Nph = (Tave / Tave). Figure 3C shows a correspondence between the average detection time and the number of incident photons. Although Figures 3A to 3C focus on the average photon acquisition time, estimating the number of incident photons is also possible using an integrated photon acquisition time. Furthermore, the averaging or integration process can be performed within the photoelectric conversion device 100 or in an external processing circuit by outputting a signal for each subframe externally from the photoelectric conversion device 100. The above-mentioned relationship between the number of incident photons and the detection time is suitable if a minimum unit of detection time is sufficiently smaller than the photon detection time, but it can have an effect if the minimum unit of detection time is approximately equal to the photon detection time. Since, for example, the expected number of incident photons can vary depending on the time of detection, even within the minimum unit of detection time, the above relationship can produce an error. A situation in which such an error is not negligible is expressed as a situation in which the acquisition time is discretely affected. Figures 4A to 4C refer to an estimate of the number of photons when the detection time is considered discrete. Figures 4A to 4C schematically illustrate a photon detection probability. If the detection time is defined as 1, 2, etc., the photon detection probability at a given time is known to follow an exponential distribution (f(t, λ) = λe - λt, where λ is the number of events per unit of time). In this case, λ is a value determined based on the number of incident photons, the exposure time, and the unit of time (i.e., the minimum unit of the detection time). Specifically, λ is equal to (number of incident photons / exposure time) × (unit of time). Assuming the number of incident photons is 1, the exposure time is 1000, and the unit of time is 1, i.e., (1 / 1000) × 1, then λ is equal to 0.001. According to this exponential function distribution, the photon detection probability can be represented as a graph in Fig. 4A if the abscissa axis is defined as the detection time.In this case, a solid line represents high illuminance, a dashed line represents medium illuminance, and a dash-dotted line represents low illuminance. An interval-wise cumulative detection probability is expressed as F(t, λ) = 1 - e-λt and can be illustrated by a graph in Fig. 4B. Furthermore, an interval-wise cumulative detection probability obtained by accumulating the detection probabilities for the respective detection intervals (0 to 1, 1 to 2, etc.) can be expressed as F'(n, λ) = F(tn, λ) + F(tn+1, λ) and can be represented by a graph shown in Fig. 4C. By performing such a calculation, a photon detection probability can be determined for each detection interval. This interval-wise cumulative detection probability and the total sum (expected value E) of the products of the corresponding detection times can be determined based on the following expression: This expected value E corresponds to the Tave shown in Fig. 3B. Based on the above calculation, the number of Nphder incident photons can be estimated using the expected value E, even if the detection time is discrete. Fig. 5A shows a specific example of the expectation value relative to the number of incident photons. Assuming the exposure period is defined as 1000 and the time unit as 1, Fig. 5A shows an output E (i.e., the expected value of the detection time) obtained when an input (i.e., the number of incident photons) changes to 1, 10, 100, and 1000, as well as an output E' (exposure time - expected value of the detection time). Figures 5B and 5C show diagrams of the input-output characteristics with respect to output E and output E', respectively. Output E forms a curve in which the output E decreases with an increasing number of incident photons. In contrast, output E' forms a curve in which the output E' increases with an increasing number of incident photons. An imaging device typically outputs a signal whose output increases with the increasing number of incident photons as input. Therefore, for subsequent signal processing, the output E' can be output instead of the output E. According to this configuration, the number of incident photons within an exposure period can be estimated from a single photon acquisition time, thus extending the dynamic range relative to the number of captured photons. Since the duration of a subframe period can be set by a photon exposure control device, adjustments can also be made to prevent a counter from saturating during a frame period. This prevents the counter from stopping during a frame period while ensuring the dynamic range is maintained, thereby preventing signal information loss. By using the technical concept described above, an additional configuration that stops the counter during a frame period can be used. The individual implementation examples are described below. First embodiment Fig. 6 shows the configuration of the multilayer photoelectric conversion device 100 according to this embodiment. The photoelectric conversion device 100 is formed by stacking two substrates, namely a first substrate 11 (sensor substrate) and a second substrate 21 (circuit substrate), and by electrically connecting the two substrates together. The first substrate 11 includes several photoelectric conversion elements 1. The circuit substrate includes a signal processor 103 circuit. Both the first substrate 11 and the second substrate 21 are described below as a single chip (diced chip), but are not limited to a single chip. For example, each substrate can be a wafer. Alternatively, the substrates can be diced after stacking in a wafer state, or they can be formed into chips that are subsequently stacked and interconnected. The first substrate 11 has a pixel area 12. The second substrate 21 has a circuit area 22 that processes a signal detected in the pixel area 12. Fig. 7 shows a layout example of the first substrate 11. The pixels 101, each having a photoelectric conversion element 1 containing an avalanche photodiode (APD), are arranged in a two-dimensional array in top view and form the pixel area 12. Fig. 8 shows the configuration of the second substrate 21. The second substrate 21 includes signal processors 103, which process electrical charges that have undergone photoelectric conversion at the photoelectric conversion elements 1, a line circuit 112, a control pulse generator device 115, a horizontal scanning circuit unit 111, a signal line 113, a vertical scanning circuit unit 110, a control line 116 and a control line 117. The pixels 101 with the photoelectric conversion elements 1 in Fig. 7 and the signal processors 103 in Fig. 8 are electrically connected via connecting wires provided for the respective pixels. Each pixel 101 and the corresponding signal processor 103 can sometimes be referred to as a pixel circuit. The vertical scanning circuit unit 110 in Fig. 8 receives a control pulse supplied by the control pulse generator 115 and delivers the control pulse to each pixel. The vertical scanning circuit unit 110 used is a logic circuit, such as a shift register or an address decoder. A signal output by each photoelectric conversion element 1 is processed by the corresponding signal processor 103. Each signal processor 103 is equipped, for example, with a counter and a memory, and the memory stores a digital value. The horizontal scanning circuit unit 111 inputs a control pulse to sequentially select each line into the corresponding signal processor 103 in order to read a signal from the memory of each pixel containing a digital signal. With respect to a selected line, a signal is output from the signal processor 103 of the pixel selected by the vertical scanning unit 110 to the signal line 113. The signal output to signal line 113 is output via an output circuit 114 to an external recording unit or a signal processor of the photoelectric conversion device 100. In Fig. 7, the photoelectric conversion elements 1 can be arranged one-dimensionally in the pixel area 12. This embodiment can also achieve its advantages when there is only one pixel, and includes the case where there is only one pixel. The function of each signal processor does not necessarily have to be provided for each of the photoelectric conversion elements. For example, a single signal processor can be shared by several photoelectric conversion elements and perform signal processing sequentially. As shown in Figures 7 and 8, several signal processors 103 are arranged in an area that overlaps the pixel area 12 in the top view. In the top view, the vertical scanning circuit unit 110, the horizontal scanning circuit unit 111, the line array circuit 112, the output circuit 114, and the control pulse generator 115 are arranged in an area that overlaps a region between the edges of the first substrate 11 and the edges of the pixel area 12. In other words, the first substrate 11 has the pixel area 12 and a non-pixel area arranged around the pixel area 12. The vertical scanning circuit unit 110, the horizontal scanning circuit unit 111, the line array circuit 112, the output circuit 114, and the control pulse generator 115 are arranged in an area that overlaps the non-pixel area in the top view. Fig. 9 shows an example of a block configuration of a pixel array or pixel matrix, the timing generator 3, and the measuring device 4. The exposure control device 2 and the timing generator 3 can be contained in the vertical scanning circuit unit 110 or the control pulse generator 115 shown in Fig. 8. A pixel circuit includes the photoelectric conversion element 1, the measuring device 4, and the pulse control device 5. The measuring device 4 consists of a signal processing circuit 201, a timing circuit 202, and a counter circuit 203. The signal processing circuit 201 is, for example, a waveform shaping circuit or a resistor or switch that is connected between a voltage applied to the photoelectric conversion element and the photoelectric conversion element. Each signal processor 103 shown in Fig. 8 corresponds to the measuring device 4 shown in Fig. 9 (i.e., the signal processing circuit 201, the timing circuit 202, and the counter circuit 203). The pulse control device 5 consists of a logic circuit 210 and a selection circuit 211. The logic circuit 210 compares a value output by the counter circuit 203 with an output of the logic circuit 210 and outputs a comparison result to the selection circuit 211. The selection circuit 211 receives several pulse signals P_TCLK1, P_TCLK2, and P_TCLK3 from the timing generator device 3 and, based on the comparison result of the selection circuit 211, selects which of the pulse signals is to be input into the timing determination circuit 202. A pulse signal P_PCLK is output by the exposure control unit 2 and input into the signal processing circuit 201. The pulse signals P_TCLK1, P_TCLK2 and P_TCLK3 are output by the timing generator unit 3, and a pulse signal selected via the selection circuit 211 is input into the timing determination circuit 202. Fig. 10A shows an example of the pixel circuit configuration. The photoelectric conversion element 1 is a single-photon avalanche photodiode (SPAD) and generates an electric charge pair according to the incident light by photoelectric conversion. The anode of the photoelectric conversion element 1 is supplied with a voltage VL (first voltage). The cathode of the photoelectric conversion element 1 is supplied with a voltage VH (second voltage), which is higher than the voltage VL applied to the anode. The anode and the cathode are supplied with a reverse bias (i.e., a voltage greater than or equal to the breakdown voltage) to cause the photoelectric conversion element 1 to perform an avalanche multiplication process. By applying such a voltage, an electric charge generated by incident light triggers an avalanche multiplication, or...- multiplication occurs, resulting in an avalanche flow. The case where a reverse bias is applied includes Geiger mode, where the potential difference between the anode and cathode is greater than the breakdown voltage, and linear mode, where the potential difference between the anode and cathode is close to, less than, or equal to the breakdown voltage. An APD operating in Geiger mode is called a SPAD. For example, the voltage VL (first voltage) is -30 V and the voltage VH (second voltage) is 1 V. The APD can operate in either linear or Geiger mode. The signal processing circuit 201 includes a quench element 204 and a waveform shaping circuit 205. The quench element 204 is connected to a power supply providing the voltage VH and to the photoelectric conversion element 1. During signal multiplication based on avalanche multiplication, the quench element 204 acts as a load circuit (quench circuit) and its function is to suppress avalanche multiplication by reducing the voltage supplied to the photoelectric conversion element 1 (quench operation). Furthermore, the quench element 204 restores the voltage supplied to the photoelectric conversion element 1 to the voltage VH by causing an electric current to flow by an amount equal to the voltage drop during the quench operation (recharge operation).The quenching element 204 can, for example, consist of a p-channel metal-oxide semiconductor transistor or an n-channel metal-oxide semiconductor (NMOS) transistor. Fig. 10A shows an example where an electrical connection is switchable by placing a switch, such as a transistor, between the power supply and the photoelectric conversion element 1. The resistance of the quenching element 204 can be a wire resistor, or the resistance can be omitted from the equivalent circuit. The waveform-shaping circuit 205 shapes a potential change obtained at the cathode of the photoelectric conversion element 1 at the time of photon detection and outputs a pulse signal. The waveform-shaping circuit 205 is, for example, an inverter circuit. Although a single inverter is used as the waveform-shaping circuit 205 in the example shown in Fig. 10A, a circuit with several inverters connected in series or another circuit with a waveform-shaping effect can also be used. The timing circuit 202 is connected to the waveform shaping circuit 205 and the counter circuit 203. The timing circuit 202 receives a signal output by the waveform shaping circuit 205 and a pulse signal P_TCLK output by the selection circuit 211, and outputs a signal to the counter circuit 203 in accordance with a combination of these signals. An example is an AND gate. The logic circuit 210 includes, for example, several threshold memories. A threshold can be set to a predetermined value. The multiple threshold memories hold or store different values ​​as reference thresholds. The logic circuit 210 compares a value output by the counter circuit 203 with the threshold stored in each of the multiple threshold memories and outputs a comparison result to the selection circuit 211. In Fig. 9 and Fig. 10A to 10C, three pulse signals P_TCLK1, P_TCLK2, and P_TCLK3 are input to the selection circuit 211, but the number of pulse signals input to the selection circuit 211 can be four or more, as long as the number of pulse signals is at least two. Fig. 10B shows the relationship between the pulse signal P_PCLK, V_ph (i.e., a cathode potential of the photoelectric conversion element 1), and P_ph (i.e., an output of the waveform shaping circuit 205) during clocked recharge driving. At time t1, the pulse signal P_PCLK transitions from a low (L) to a high (H) level. When the switch is on, the cathode terminal of the photoelectric conversion element 1 is electrically connected to the supply voltage, and a reverse bias is applied to the photoelectric conversion element 1. Specifically, a state in which the pulse signal P_PCLK is at a high level and the switch is in the on-mode is a recharge mode. Because the recharge mode is repeated multiple times, this state is also called the recharge mode. When the reverse bias is applied, the cathode potential V_ph increases.When the cathode potential V_ph exceeds a threshold value for detection, the output P_ph transitions from a high (H) level to a low (L) level. Subsequently, the pulse signal P_PCLK transitions from a high (H) level to a low (L) level, and the photoelectric conversion element 1 enters a standby mode to await the arrival of photons. If a photon arrives at time t2, the cathode potential V_ph decreases. If the cathode potential V_ph exceeds the threshold value for detection at time t3, the output P_ph transitions from a low (L) level to a high (H) level. Subsequently, the pulse signal P_PCLK transitions again from a low (L) level to a high (H) level at time t4, the switch is turned on, and the process described above is repeated. This clocked recharging control ensures that even if a large number of photons are received in standby mode, at least one output signal can be counted, thus making this control effective as a countermeasure against pile-up. Fig. 10C shows a truth table that specifies an output P_sig with respect to an input P_ph and a pulse signal P_TCLK to the timing circuit 202. 0 indicates the low level, and 1 indicates the high level. Since the timing circuit 202 consists of an AND gate, the output P_sig is only at the high level if the input P_ph and the pulse signal P_TCLK are both at the high level. Fig. 11 shows a timing diagram to explain the exposure period and the pulse signals. A frame period consists of N subframes. The start and end of each subframe are determined by the pulse signal P_PCLK. A subframe contains pulses selected from the pulse signals P_TCLK1 to P_TCLK3. The pulse signal P_TCLK1 contains M pulses within a subframe, the pulse signal P_TCLK2 contains N pulses within a subframe, and the pulse signal P_TCLK3 contains O pulses within a subframe. In this case, the number of pulses satisfies the relationship M > N > O. The pulses are input into the timing control circuit 202. In Fig. 11, the pulses of each pulse signal P_TCLK are arranged at non-uniform intervals, with the intervals being proportional to an approximate logarithm. As described below, the pulses of the individual pulse signals P_TCLK can be arranged at uniform intervals.Alternatively, the pulses can be arranged at irregular intervals that are proportional to an approximate inverse. Fig. 11 shows a diagram illustrating the concept described above in Figs. 3A to 3C. A pulse of the pulse signal P_PCLK serves as the start point of a subframe, and an interval of the subframe is Tacc. The output P_ph transitions from a low level to a high level when a photon is incident and, in accordance with the recharging process of the photoelectric conversion element 1, transitions from a high level to a low level when a pulse of the pulse signal P_PCLK is input. A pulse signal P_TCLK serves to define timing information within a subframe. In accordance with the configuration of the timing control circuit 202 described in Figures 10A to 10C, the number of pulse signals P_TCLK at or after the first photon acquisition within a subframe is a count value. The timing control circuit 202 outputs a pulse signal at or after the first photon acquisition time within a subframe period. In Fig. 11, a signal P_sig is input into a counter in a first subframe (A), and a value of six is ​​counted by the counter. Accordingly, the counter's count is high when a photon arrives at the beginning of a subframe, while the counter's count is low when a photon arrives at the end of a subframe. In other words, based on a pulse signal P_TCLK, a numerical value can be measured that corresponds to the time between the start of a subframe and the first detection of a photon. By adding up the count values, repeating this count N times, a count value can be obtained that corresponds to an expected value E' of the detection time. Accordingly, as described above, the number of incident photons can be estimated from the expected value E'. According to this configuration, the number of incident photons within the exposure period can be estimated from the photon detection time, thus extending the dynamic range in proportion to the number of detected photons. Since the duration of a subframe period can be set by an exposure control device, an adjustment can also be made to prevent a counter from saturating during a frame period. This prevents the counter from stopping during a frame period while ensuring the dynamic range is maintained, thereby preventing signal information from being lost. In the prior art clocked recharge control, where the timing control circuit 202 is not provided, the number of subframe periods is the maximum number of photons that can be counted in a frame period. For example, if the number of subframes is N, the maximum count is N, so that a maximum of N photons can be detected. The dynamic range (defined as the maximum output value) is N. Since power consumption is proportional to the number of detections, the dynamic range decreases if the number of detections is reduced to achieve lower power consumption. Conversely, increasing the dynamic range results in higher power consumption. In other words, there is a trade-off between dynamic range and power consumption. On the other hand, in the photoelectric conversion device 100 according to this embodiment, which is equipped with the timing control circuit 202, the estimated number of photons corresponds to the dynamic range. Although the power consumption is proportional to the number of detections, as in the prior art, the trade-off between the dynamic range and the power consumption can be eliminated, since the estimated number of photons does not depend on the number of detected photons. Since the number of pulses of the pulse signal P_TCLK can be changed depending on the count value in this embodiment, the dynamic range can be further expanded without increasing the number of bits. In Fig. 10A, for example, the threshold values ​​of a first threshold memory, a second threshold memory, and a third threshold memory are set to "14", "126", and "510", respectively. In the first subframe, the selection circuit 211 selects the pulse signal P_TCLK1 and inputs the pulse signal P_TCLK1 as a pulse signal P_TCLK into the timing control circuit 202. If a pixel value output by the counter circuit 203 in a previous subframe within a frame is one of the values ​​0 to 14, which serves as a predetermined value, the pulse signal P_TCLK1 is entered as pulse signal P_TCLK in a subsequent subframe into the timing control circuit 202. If the pixel value output by counter circuit 203 in the preceding subframe within a frame is one from 15 to 126 that serves as a predetermined value greater than 14, the pulse signal P_TCLK2 is input as pulse signal P_TCLK in the subsequent subframe into the timing circuit 202. Pulse signal P_TCLK2 has fewer pulses per subframe than pulse signal P_TCLK1. If the pixel value output by counter circuit 203 in the preceding subframe within a frame is one of the values ​​127 to 510, the pulse signal P_TCLK3 is input as pulse signal P_TCLK in the subsequent subframe into the timing control circuit 202. Pulse signal P_TCLK3 has fewer pulses per subframe than pulse signal P_TCLK2. If the pixel value output by counter circuit 203 in the preceding subframe within a frame is greater than 511, a pulse signal P_TCLK4 is input as pulse signal P_TCLK in the subsequent subframe into the timing control circuit 202. Pulse signal P_TCLK4 has fewer pulses per subframe than pulse signal P_TCLK3. This configuration allows the dynamic range to be extended without increasing the number of bits in the counter circuit 203, which is included in the measuring device 4. The following description relates to an imaging scene in which high brightness is achieved only during a short period within a frame period, while low brightness is maintained during the remaining periods. In a subframe corresponding to high brightness, the count value is smaller than the actual number of incident photons. In a subframe corresponding to low brightness, the count value is close to the actual number of incident photons.Since linear correctors assume a uniform number of incident photons per frame period, the effect of a photon count loss in the subframe corresponding to high brightness is significant, and the corrected pixel value becomes lower than the brightness perceived by the human eye. To mitigate this problem, the count value in each subframe is incremented during periods when the pixel value within a frame is low, ensuring that a sufficient count value is achieved even in a high-brightness scene only for a short period within a frame period. Although in Fig. 11 the pulse signal P_TCLK1 is input as pulse signal P_TCLK into the timing circuit 202 in the first subframe within a frame, the configuration is not limited to this. For example, the pulse signal P_TCLK2 can be input as pulse signal P_TCLK into the timing circuit 202 in the first subframe within a frame. In this case, if the pixel value output by the counter circuit 203 is less than 15, which serves as the predetermined value (i.e., less than or equal to 14), the pulse signal P_TCLK1 can be input as pulse signal P_TCLK into the timing circuit 202 in the subsequent subframe. P_TCLK with uniform intervals and P_TCLK with non-uniform intervals Fig. 12 shows a schematic comparison diagram between a pulse signal P_TCLK with regular intervals and a pulse signal P_TCLK with irregular intervals. The upper part of Fig. 13A shows an example where a subframe has 16 regularly spaced pulses. Regularly spaced pulses correspond to real time. The lower part shows an example where the irregularly spaced pulses are set to an approximate logarithm (base 2) of real time. The reason for the inclusion of the word "approximate" is as follows: While the logarithm of 1 is equal to 0 when 2 is set as the base, and the logarithm of 2 is equal to 1 when 2 is set as the base, the irregularly spaced pulses are set to 1 and 2, respectively, by adding 1 to them, in order to compare them with the regularly spaced pulses in Fig. 13A.The intervals of these irregularly spaced pulses are set such that the pulse space corresponds to a logarithmic compression of real space. The intervals of an irregularly spaced pulse signal can be configured so that the period increases according to the elapsed time in a subframe. Figure 13B shows a diagram illustrating the relationship between the count value (output) and the number of incident photons (input) with respect to uniformly spaced pulses. As shown in Figure 13B, when comparing the same number of incident photons (input), the output of non-uniformly spaced pulses is smaller than the output of uniformly spaced pulses. In other words, non-uniformly spaced pulses allow the same number of incident photons to be determined based on a smaller count value. Thus, non-uniformly spaced pulses allow for a smaller counter circuit, thereby reducing the pixel area. On the other hand, with uniformly spaced pulses, the average interval between pulses can be reduced, resulting in a relatively higher signal-to-noise ratio (S / N) compared to non-uniformly spaced pulses. Second embodiment This embodiment relates to a configuration example with a pixel circuit that differs from that of the first embodiment. Since components other than those described below are essentially identical to those of the first embodiment, their description is omitted. A pixel circuit shown in Fig. 14A according to this embodiment differs from the pixel circuit shown in Fig. 10A in that the switch which receives the pulse signal P_PCLK and is provided between the supply voltage and the photoelectric conversion element 1 is omitted, and a latching circuit 206 is added to the signal processing circuit 201. The pulse signal P_PCLK is fed to the latching circuit 206. In the example shown in Fig. 14A, the erase element 204 used can also be a resistor. Therefore, the erase element 204 used can be not only a metallic resistor, but also, for example, a transistor. Fig. 14B shows a change in the cathode potential V_ph of the photoelectric conversion element 1 shown in Fig. 14A. The difference from Fig. 10B is that the voltage automatically returns to an initial state after the cathode potential has dropped due to photon incidence. This pixel operation is called passive operation. Fig. 15 shows a control timing diagram according to this embodiment. In Fig. 15, one of the pulse signals P_TCLK1 to P_TCLK3 is designated as P_TCLK. The difference from Fig. 11 is that the output P_ph switches between high and low multiple times in a subframe, corresponding to the photon incidence. However, since an output P_out, which is output by the latch circuit 206 and input into the timing control circuit 202, corresponds to the output P_ph in Fig. 11, the ultimately output P_sig is the same. Similar advantages to the first embodiment can be achieved with such a passively controlled ADP element. In particular, this configuration allows the number of incident photons within the exposure period to be estimated from the photon acquisition time, thus extending the dynamic range relative to the number of captured photons. Since the duration of a subframe period can be set by a photon exposure control unit, adjustments can also be made to prevent a counter from saturating during a frame period. This prevents the counter from stopping during a frame period while ensuring the dynamic range is maintained, thereby preventing signal information loss. Since the estimated number of photons corresponding to the dynamic range does not depend on the detected number of photons corresponding to the power consumption, this configuration also eliminates the trade-off relationship between the dynamic range and the power consumption. Third example This embodiment relates to a configuration equipped with a pixel circuit that differs from those in the preceding embodiments. The pixel circuit shown in Fig. 16 according to this embodiment differs from the pixel circuit shown in Fig. 10A in that it is additionally provided with a signal selection circuit 207 and a signal holding circuit 208. By adding these circuits, a signal that is to be input into the counter circuit in an M-th subframe can be switched to P_out or P_ph by referring to information indicating whether or not a photon has occurred in an (M-1)-th subframe. Since an output in a subsequent subframe is changed in accordance with the result in a preceding subframe, this circuit is called a "time correlation filter". Figure 17 shows an operating sequence according to this embodiment. Since no photon arrives in the M-th subframe, the output P_ph is at a low level. This low-level information is stored in the signal-holding circuit 208. Subsequently, when P_PCLK, which defines the start of an (M+1)th subframe, transitions from low to high level, a low-level signal is output by the signal holding circuit 208, and this low-level signal is input into the signal selection circuit 207. Accordingly, the signal selection circuit 207 is configured to output P_ph as P_sig without outputting P_out as P_sig. When the photon incident occurs in the (M+1)th subframe, P_ph transitions from low to high level, causing P_sig to also transition from low to high level. Because P_ph transitions from low to high level, the high-level information is retained in the signal holding circuit 208. Subsequently, when P_PCLK, which defines the start of an (M+2)th subframe, transitions from low to high level, P_ph transitions from high to low level, and P_sig transitions from high to low level. The level transition of P_PCLK causes a high-level signal to be output by the signal-hold circuit 208, and the signal selector circuit 207 outputs P_out as P_sig. In other words, the signal selector circuit 207 is configured to be able to output a signal corresponding to a pulse signal that defines timing information within the (M+2)th subframe period. When a photon incident occurs in the (M+2)th subframe, P_ph transitions from low to high level, so that P_out is output as P_sig. Figure 18 shows an operating sequence to explain the effect of the time correlation filter. The time correlation filter exhibits an effect when a signal of approximately one count or less is processed in a subframe. This is because the photon incidence probability becomes constant over time, based on an exponential distribution function, as the photon incidence frequency decreases. In other words, the probability of incidence in each time window becomes essentially the same. In Fig. 18, a photon arrives in a second subframe. If a photon arrives at the time shown in Fig. 18, P_sig is counted as one if a time correlation filter is present, and P_sig is counted as three if no time correlation filter is present. When a signal of approximately one count or less in a subframe is processed in this way, the configuration without a time correlation filter results in a larger number of incident photons being counted than the actual number of incident photons, leading to an error in a low-illuminance region. In other words, this can lead to an increase in noise. In contrast, in this embodiment, when a signal of approximately one count or less in a subframe is processed, the signal is counted as only one count unless the signal is continuously acquired, thus suppressing an error and reducing the noise increase factor. Consequently, the signal-to-noise ratio can be improved in a low-output region. Furthermore, since the dark count rate (DCR) is reduced, the DCR is also reduced.Since the "dark count rate", DCR) in the dark state also corresponds to a signal of approximately one count or less in a subframe, the use of this time correlation filter enables the aforementioned reduction based on the same theory. As an alternative to the circuit described above, which outputs a count value if the signal is not continuously detected, the circuit can output a predetermined value, where the predetermined value is a value greater than or equal to a count value. Fourth embodiment A fourth embodiment is now described with reference to Figs. 19 and 20. This embodiment differs in that it has three layers. In Fig. 19 a third substrate 31 (third substrate) and a second circuit area 32 have been added. Fig. 20 schematically shows the layout of a three-layer pixel circuit. Compared to the pixel circuit in Fig. 10A, a second timing control circuit 302, a second counter circuit 303, a second logic circuit 310, and a second selection circuit 311, which serves as a second pulse control device, have been added, and these circuits are arranged in the third substrate 31. The second timing control circuit 302 is configured to receive a pulse signal selected by the second selection circuit 311 and an output from the waveform shaping circuit 205. In Fig. 20, it is assumed that the vertical scanning circuit unit 110 and the control pulse generator unit 115 are provided in the second substrate 21, so that the pulse signals P_TCLK1 to P_TCLK4 are input into the third substrate 31 by the circuits provided in the second substrate 21. By omitting the erase element 204 and the waveform shaping circuit 205, the third substrate 31 can save space compared to the second substrate 21. Thus, the third substrate 31 can be equipped with the vertical scanning circuit unit 110 and the control pulse generator unit 115. In this case, the pulse signal P_PCLK and the pulse signals P_TCLK1 to P_TCLK4 can be input from the third substrate 31 into the second substrate 21. In this embodiment, the thresholds to be set in the first to third threshold memories of logic circuit 210 and the thresholds to be set in the second logic circuit 310 can vary. For example, the thresholds in the first to third threshold memories of logic circuit 210 can be set to low values, and the thresholds in the first to third threshold memories of the second logic circuit 310 can be set to higher values ​​than those in the threshold memories of logic circuit 210. If two counters have a different number of bits, it is possible to use the implemented bit width effectively by setting separate thresholds for each. The three-layer stacked structure in this embodiment allows multiple circuits to be easily parallelized, thus enabling extended functionality. Specifically, the timing control circuits 202 and 302 can be connected in parallel, allowing two outputs with different count values ​​to be obtained from a single photon detection signal by using the pulse signals P_TCLK1 and P_TCLK2 with different waveforms. Depending on the number of pulses and the pulse intervals of the pulse signal P_TCLK, the advantages and disadvantages of various characteristics (e.g., dynamic range, signal-to-noise ratio, suitable exposure quantity, and power consumption) vary. With two outputs with different characteristics, an optimal output can be selected depending on the imaging scene, or the outputs can be combined to produce a higher-quality image. For example, if the measurement is to be performed using a pulse signal P_TCLK as in the first embodiment, the anticipated problem is that the measurement error can increase in an imaging scene where the amount of light changes rapidly within a frame. This is because the difference between the measured values ​​at the photon acquisition times of the respective subframes is large when average light is incident within a frame. One method for solving this problem is to simultaneously acquire a signal that allows an estimation of the change in the amount of light within a frame and to perform a correction. Specifically, this can be achieved, for example, by performing a count while limiting the pulse signal P_TCLK2 to the first single pulse, in order to count only incident photons at an early acquisition time. The threshold values ​​in the first to third threshold memories of the logic circuit 210 and the threshold values ​​in the first to third threshold memories of the second logic circuit 310 can be set to identical values. Fifth embodiment A photoelectric conversion system using the photoelectric conversion device according to one of the above embodiments is now described with reference to Fig. 21. Fig. 21 shows a block diagram schematically illustrating the configuration of the photoelectric conversion system according to this embodiment. A processing device according to this embodiment includes a control device 401, a timing adjustment device 402, an image acquisition device 403, a reading device 404, a gain adjustment device 405, a nonlinear correction device 406, a defect correction device 407, a data compression device 408 and a storage unit 409. The image acquisition device 403 is, for example, a pixel circuit, and the reading device 404 is, for example, connected downstream of the counter circuit 203. The control device 401 can be an internal control device of the photoelectric conversion device or an external control device of the photoelectric conversion device. The image acquisition device 403 is controlled by the timing adjustment device 402, which is controlled by the control device 401. The image data generated by the image acquisition device 403 is entered into the storage unit 409 after undergoing correction processing. The sequence of correction processing is not limited to the sequence shown in Fig. 21. The gain matching device 405 is located between the reading device 404 and the nonlinear correction device 406 and applies digital gain to the image data generated by the image acquisition device 403. Although image correction data often has a fractional value, the correction accuracy can decrease due to quantization error if the image output is an integer. By applying gain to the image data beforehand, the effect of the quantization error can be suppressed, thus improving the correction accuracy. If the quantization error can be reduced to a quarter or less of a one-photon signal level, the corrected image will appear visually natural. Therefore, it is desirable for the digital gain applied to the image data to be, for example, four times or more. The nonlinear correction device 406 is located between the gain adjustment device 405 and the defect correction device 407 and corrects the image data by being controlled by the control device 401. If the image acquisition device 403 is a photon-counting acquisition device, the optical response is often nonlinear due to the dead-time effect. The effect of a nonlinear optical response can sometimes lead to overcorrection if a correction is performed assuming a linear response. Therefore, by performing a nonlinear correction on the image data before arithmetic processing in the defect correction device 407, overcorrection is prevented, allowing for appropriate nonlinear correction to be performed according to the drive timing. This nonlinear correction is performed, for example, using a lookup table.The nonlinear correction device 406 includes a correction circuit that corrects a signal output by the image acquisition device 403. The correction circuit modifies a correction method according to the pulse signal number selected by the selection circuit 211 in a pixel. For example, if the pulse signal P_TCLK2 is selected in a subframe, a pixel value is corrected such that the correction amount is greater than if the pulse signal P_TCLK1 were selected. Conversely, if the pulse signal P_TCLK1 is selected in a subframe, a pixel value is corrected such that the correction amount is smaller than if the pulse signal P_TCLK2 were selected. Because the number of pulses input in a subframe decreases at high illuminance, the output may be lower than the original brightness at high illuminance.According to this embodiment, the correction is appropriately carried out so that the dynamic range can be extended at high illuminance. The Defect Correction Unit 407 corrects defective or faulty pixel data contained in the image data. As a specific example, the Defect Correction Unit 407 extracts an output value from a defective pixel and identifies positional information and the output value of the defective pixel. The methods include a procedure in which the output of pixels surrounding an identified defective pixel is replaced by an average or median value, and a procedure in which a division is performed by estimated defective image data. The data compression device 408 compresses the corrected image data. In the photoelectric conversion device according to the present invention, an enormous amount of image data corresponding to a high dynamic range is generated. By providing the data compression device 408, the data can be compressed before being stored in the downstream storage unit 409. The memory unit 409 stores at least a portion of the previously generated image data. Specifically, the memory unit 409 used to store the image data is a type of memory, such as static random access memory (SRAM), dynamic random access memory (DRAM), or non-volatile memory. Accordingly, with this embodiment, a photoelectric conversion system can be achieved using the photoelectric conversion device according to one of the preceding embodiments. Sixth embodiment The advantages of the present invention are described in more detail with reference to Figures 22A and 22B. In the following description, the addition performed in each of the preceding embodiments is referred to as the "weighted counting method". In a prior art clocked recharging method, shown in Fig. 22A, the maximum estimated number of incident photons is determined by the number of recharging CLKs (P_PCLKs). In particular, the dynamic range increases with an increasing number of recharging CLKs. However, since the power consumption also increases proportionally to the number of recharging CLKs, there is a trade-off between the dynamic range and the power consumption. If an exposure period is defined as T and a pulse interval of the recharge CLK as Δtr, the number of recharge CLKs is expressed as T / Δtr, so that it can be assumed that the dynamic range is determined by T / Δtr. In contrast, the weighted counting method shown in Fig. 22B estimates the number of incident photons from the time of photon incidence. Therefore, the maximum estimated number of incident photons is determined by T / Δtw. In this case, Δtw denotes a period from the input of a pulse from a recharge CLK (P_PCLK in the exemplary embodiment) to the input of the first pulse from P_TCLK. In particular, the maximum estimated number of incident photons is not dependent on the recharge CLK interval Δtr, and the dynamic range and power consumption are not in a trade-off relationship. In this case, the weighting coefficient (an increment of the count corresponding to the arrival of a photon) is conveniently set to Δtr / Δtw. A concrete numerical example is given below. In the prior art method, when the exposure period T is set to 1024 and Δtr to 1, the maximum number of avalanche events is 1024, and in this case, the maximum number of detected incident photons is also 1024. In contrast, with the weighted counting method, when the exposure period T is set to 1024, Δtr to 4, and Δtw to 1, the maximum number of avalanche events is 256. If the counter circuit is adjusted such that the counter number corresponding to the photons incident during Δtw is four (Δtr / Δtw), then the maximum number of incident photons at this time is 1024. In other words, the power consumption associated with recharging can be reduced to a quarter of that of the prior art method, while achieving a similar dynamic range.In each of the above embodiments, the addition of four at time Δtw can be achieved by, for example, inputting four pulses of P_TCLK in a period that is sufficiently shorter than Δtw. The weighting coefficient is preferably set to Δtr / Δtw, since under drive conditions where both methods have similar dynamic ranges, the saturation count can be aligned. Setting such conditions allows for the reduction of false signals and the like during nonlinear correction. However, since the power consumption depends only on Δtr and not on the weighting coefficient, the ratio expression given above does not necessarily have to be satisfied from the perspective of power consumption suppression. Seventh embodiment A photoelectric conversion system according to this embodiment is now described with reference to Fig. 23. Fig. 23 shows a block diagram that schematically represents the configuration of the photoelectric conversion system according to this embodiment. The photoelectric conversion device described in the preceding embodiments is suitable for various photoelectric conversion systems. Examples of applicable photoelectric conversion systems include a digital still camera, a digital camcorder, a surveillance camera, a photocopier, a facsimile machine, a mobile phone, a vehicle camera, and a surveillance satellite. A camera module, comprising an optical system such as a lens and an imaging device, is also included in the photoelectric conversion system. The block diagram shown in Fig. 23 corresponds to a digital camera as one of the preceding examples. The photoelectric conversion system shown in Fig. 23 includes an imaging device 1004, as an example of a photoelectric conversion device, and a lens 1002, which produces an optical image of an object on the imaging device 1004. The photoelectric conversion system further includes an aperture 1003 for changing the amount of light transmitted through the lens 1002 and a barrier 1001 for protecting the lens 1002. The lens 1002 and the aperture 1003 form an optical system that focuses light onto the imaging device 1004. The imaging device 1004 is the photoelectric conversion device according to one of the preceding embodiments and converts the optical image produced by the lens 1002 into an electrical signal. The photoelectric conversion system includes a signal processor 1007, which acts as an image generator and produces an image by processing an output signal provided by the imaging device 1004. The signal processor 1007 may perform various types of correction and compression and output image data. The signal processor 1007 can be provided in the same semiconductor layer as the imaging device 1004, or it can be provided in a different semiconductor layer. Alternatively, the imaging device 1004 and the signal processor 1007 can be provided in the same semiconductor layer. The photoelectric conversion system further includes a memory 1010 for temporarily storing image data and an external interface (external I / F) 1013 for communicating with, for example, an external computer. In addition, the photoelectric conversion system includes a recording medium 1012, such as a semiconductor memory, for recording or reading image data, and a recording medium control interface (recording medium control I / F) 1011 for recording to or reading from the recording medium 1012. The recording medium 1012 can be contained within the photoelectric conversion system or be removable from it. The photoelectric conversion system further includes a central control unit 1009, which performs various types of calculations and controls the entire digital still camera, and a timing generator 1008, which outputs various types of timing signals to the imaging device 1004 and the signal processor 1007. A timing signal, or time signal, and the like, can be input externally, and the photoelectric conversion system can include at least the imaging device 1004 and the signal processor 1007, which processes an output signal issued by the imaging device 1004. The imaging device 1004 outputs an imaging signal to the signal processor 1007. The signal processor 1007 performs a predetermined signal processing on the imaging signal output by the imaging device 1004 and outputs image data. The signal processor 1007 uses the image signal to generate an image. Accordingly, with this embodiment, a photoelectric conversion system can be implemented using the photoelectric conversion device (imaging device) according to one of the preceding embodiments. Eighth example A photoelectric conversion system and a mobile object according to this embodiment are now described with reference to Figs. 24A and 24B. Figs. 24A and 24B show the configurations of the photoelectric conversion system and the mobile object according to this embodiment. Fig. 24A shows an example of a photoelectric conversion system in conjunction with a vehicle camera or in-vehicle camera. A photoelectric conversion system 2300 includes an imaging device 2310. The imaging device 2310 is the photoelectric conversion device according to one of the preceding embodiments. The photoelectric conversion system 2300 includes an image processor 2312, which performs image processing on multiple parts of image data acquired by the imaging device 2310. The photoelectric conversion system 2300 further includes a parallax detection device 2314, which calculates parallax (i.e., a phase difference of parallax images) from the multiple parts of the image data acquired by the photoelectric conversion system 2300.Furthermore, the photoelectric conversion system 2300 includes a distance sensing device 2316, which calculates a distance to a target object based on the calculated parallax, and a collision detection device 2318, which determines whether there is a possibility of collision based on the calculated distance. The parallax sensing device 2314 and the distance sensing device 2316 are an example of a distance information acquisition unit that acquires distance information to a target object. In particular, the distance information can be acquired not only using a phase difference but also using time-of-flight (ToF) technology. The collision detection device 2318 can determine a possibility of collision using either of these distance information values.The distance information acquisition unit can be implemented using custom-developed hardware or a software module. Alternatively, the distance information acquisition unit can be implemented, for example, using a field-programmable (logic) gate array (FPGA), an application-specific integrated circuit (ASIC), or a combination thereof. The photoelectric conversion system 2300 is connected to a vehicle information acquisition device 2320 and can acquire vehicle information such as vehicle speed, yaw rate, and steering angle. The photoelectric conversion system 2300 is connected to a control ECU (electronic control unit) 2330, which acts as a control device that outputs a control signal to cause a vehicle to generate a braking force based on a determination result obtained from the collision detection device 2318. Furthermore, the photoelectric conversion system 2300 is also connected to a warning device 2340, which issues a warning to a driver based on the determination result obtained from the collision detection device 2318.For example, if the determination result obtained from the collision detection device 2318 indicates a high probability of a collision, the control ECU 2330 performs vehicle control to avoid the collision or to mitigate the damage by applying a braking force, releasing the accelerator pedal, suppressing engine power, or similar actions. The warning device 2340 warns the user by, for example, sounding an audible alarm or similar, displaying warning information on a screen of a vehicle navigation system or similar, and / or vibrating the seat belt and / or the steering wheel. In this embodiment, the photoelectric conversion system 2300 captures an image of an area in the vicinity of the vehicle, e.g., an image of an area in front of or behind the vehicle. The photoelectric conversion system shown in Fig. 24B relates to a case in which an image of an area in front of the vehicle (imaging area 2350) is to be captured. The vehicle information acquisition device 2320 transmits a command to the photoelectric conversion system 2300 or the imaging device 2310. With such a configuration, the accuracy of the distance measurement can be further improved. Although the preceding description concerns an example where control is performed to avoid a collision with another vehicle, the photoelectric conversion system is also applicable to autonomous driving control for tracking another vehicle or autonomous driving control for preventing lane changes. Furthermore, the photoelectric conversion system is not limited to a vehicle, such as a host vehicle, and can be applied, for example, to a mobile object (mobile device), such as a ship, an aircraft, or an industrial robot. Moreover, the photoelectric conversion system is not limited to a mobile object and can be applied to a device that makes extensive use of object recognition, such as an intelligent transportation system (ITS). Ninth embodiment A photoelectric conversion system according to this embodiment is now described with reference to Fig. 25. Fig. 25 shows a block diagram illustrating a configuration example of a distance image sensor serving as a photoelectric conversion system. As shown in Fig. 25, a distance image sensor 1401 includes an optical system 1402, a photoelectric conversion device 1403, an image processing circuit 1404, a monitor 1405, and a memory 1406. The distance image sensor 1401 receives light (modulated or pulsed light) projected onto an object by a light source device 1411 and reflected from the surface of the object to capture a distance image corresponding to the distance to the object. The optical system 1402 includes one or more lenses, directs image light (incident light) from the object to the photoelectric conversion device 1403 and causes an image to be formed on a light receiving surface (sensor) of the photoelectric conversion device 1403. The photoelectric conversion device 1403 is the photoelectric conversion device according to one of the preceding embodiments. A distance signal, which indicates a distance determined from a light reception signal output by the photoelectric conversion device 1403, is supplied to the image processing circuit 1404. The image processing circuit 1404 performs image processing, which includes generating a distance image based on the distance signal supplied by the photoelectric conversion device 1403. The distance image (image data) obtained as a result of the image processing is fed to the monitor 1405 for display or to the memory 1406 for storage (recording). The 1401 distance image sensor, which has this configuration, uses the aforementioned photoelectric conversion device to achieve improved pixel characteristics and thereby, for example, to capture a more accurate distance image. Tenth embodiment A photoelectric conversion system according to this embodiment is now described with reference to Fig. 26. Fig. 26 shows an example of a schematic configuration of an endoscopic surgical system that serves as a photoelectric conversion system according to this embodiment. In Fig. 26, a surgeon (doctor) 1131 performs an operation on a patient 1132 on a patient bed 1133 using an endoscopic surgical system 1103. As shown in Fig. 26, the endoscopic surgical system 1103 includes an endoscope 1100, a surgical instrument 1110, and a cart 1134 equipped with various devices for endoscopic surgery. The endoscope 1100 includes a lens tube 1101, the portion of which, at a predetermined length from its distal end, is to be inserted into the patient's body cavity 1132, and a camera head 1102, which is connected to the base end of the lens tube 1101. Although the endoscope 1100 in the example shown in Fig. 26 is a so-called rigid endoscope with a rigid lens tube 1101, the endoscope 1100 can also be a so-called flexible endoscope with a flexible lens tube. The distal end of the lens tube 1101 is provided with an opening into which an objective lens is inserted. The endoscope 1100 is connected to a light source device 1203. The light generated by the light source device 1203 is optically guided to the distal end of the lens tube 1101 by a light guide extending into the lens tube 1101 and projected via the objective lens onto a target in the patient's body cavity 1132. The endoscope 1100 can be a forward-viewing endoscope, an oblique-viewing endoscope, or a side-viewing endoscope. An optical system and a photoelectric conversion device are provided within the camera head 1102, and reflected light (observation light) from the observation target is focused by the optical system onto the photoelectric conversion device. The observation light is photoelectrically converted by the photoelectric conversion device, so that an electrical signal corresponding to the observation light, i.e., an image signal corresponding to an observation image, is generated. The photoelectric conversion device can be the photoelectric conversion device according to any of the preceding embodiments. The image signal is transmitted as raw data to a camera control unit (CCU) 1135. The CCU 1135 consists of a central processing unit (CPU), a graphics processing unit (GPU), or similar components, and centrally controls the operation of the endoscope 1100 and a display device 1136. Furthermore, the CCU 1135 receives the image signal from the camera head 1102 and performs various types of image processing, such as demosaicing, on the image signal to display an image based on the signal. Controlled by the CCU 1135, the display device 1136 shows the image based on the image signal processed by the CCU 1135. The light source device 1203 includes a light source, such as a light-emitting diode (LED), and supplies the endoscope 1100 with irradiation light when a surgical area is to be imaged. An input device 1137 is an input interface for the endoscopic surgical system 1103. A user can use the input device 1137 to input various types of information or a command into the endoscopic surgical system 1103. An instrument control device 1138 controls the actuation of an energy treatment instrument 1112 for cauterizing tissue, cutting tissue, sealing a blood vessel or the like. The light source device 1203, which provides irradiation light when a surgical area is to be imaged in the endoscope 1100, can, for example, include a white light source including an LED, a laser light source, or a combination thereof. If the white light source consists of a combination of red, green, and blue laser light sources, the output intensities and output times of the corresponding colors (corresponding wavelengths) can be controlled with high accuracy, so that the white balance of a captured image can be adjusted in the light source device 1203. Furthermore, in this case, the laser beams from the red, green, and blue laser light sources can be projected onto the observation target in a temporally separated manner, and the control of an imaging element or...The imaging element of the camera head 1102 can be controlled synchronously with the irradiation times of the laser beams, enabling the time-separated acquisition of images corresponding to the respective R, G, and B colors. This method allows a color image to be obtained without the need for a color filter on the imaging element. The light source device 1203 can be controlled such that the intensity of the emitted light changes in each predetermined time period. By controlling the imaging element of the camera head 1102 synchronously with the time of the change in light intensity, capturing images in time-split intervals, and combining the images, a so-called high dynamic range image without black crush or white clipping can be generated. The light source device 1203 can be capable of providing light in a predetermined wavelength band corresponding to special lighting observation. Special lighting observation utilizes, for example, the wavelength dependence of light absorption in body tissue. Specifically, the emitted light lies in a narrower band than the irradiation light used in normal observation (i.e., white light), so that predetermined tissues, such as superficial mucosal vessels, are imaged with high contrast. Alternatively, special light observation can also be performed as a fluorescence observation to obtain an image of the fluorescence that occurs as a result of irradiation with excitation light. Fluorescence observation can, for example, consist of irradiating body tissue with excitation light and observing the fluorescence of the body tissue, or obtaining a fluorescence image by locally injecting a reagent such as indocyanine green (ICG) into the body tissue and irradiating the body tissue with excitation light corresponding to the fluorescence wavelength of the reagent. The light source device 1203 can be capable of providing narrowband light and / or excitation light corresponding to such special light observation. Eleventh embodiment A photoelectric conversion system according to this embodiment is now described with reference to Fig. 27A and Fig. 27B. Fig. 27A shows an example of the configuration of a pair of glasses (smartglasses) 1600, which serves as a photoelectric conversion system. The glasses 1600 include a photoelectric conversion device 1602. The photoelectric conversion device 1602 is the photoelectric conversion device according to one of the preceding embodiments. The rear side of a lens 1601 can be provided with a display device that includes a light-emitting device, such as an organic LED (OLED) or an LED. The photoelectric conversion device 1602 can be a single device or multiple devices. Furthermore, several types of photoelectric conversion devices can be used in combination. The arrangement position of the photoelectric conversion device 1602 is not limited to that shown in Fig. 27A. The spectacle 1600 further includes a control device 1603. The control device 1603 acts as a power supply, providing electrical current to the photoelectric conversion device 1602 and the aforementioned display device. The control device 1603 also controls the operation of the photoelectric conversion device 1602 and the display device. The lens 1601 is equipped with an optical system for focusing light onto the photoelectric conversion device 1602. Fig. 27B shows smart glasses 1610 according to an application example. The glasses 1610 include a control device 1612. The control device 1612 includes a photoelectric conversion device, equivalent to the photoelectric conversion device 1602, and a display device. A lens 1611 is equipped with an optical system for projecting light emitted by the photoelectric conversion device within the control device 1612 and by the display device, so that an image is projected onto the lens 1611. The control device 1612 acts as a power supply, providing electrical current to the photoelectric conversion device and the display device, and also controls the operation of the photoelectric conversion device and the display device. The control device 1612 may include a line-of-sight detection device that detects the wearer's line of sight.Infrared light can be used to detect the line of sight. An infrared emitter emits infrared light towards the eyeball of a user looking at a display image. An imaging device with a photoelectric conversion element detects reflected light from the emitted infrared light and the eyeball to obtain an image of the eyeball. A reduction unit is provided to reduce the light from the infrared emitter to a top-down display unit, thus preventing a decrease in image quality. The user's line of sight relative to the displayed image is determined from the captured eyeball image obtained by imaging infrared light. Any known technique can be used for line-of-sight detection using this captured eyeball image. One example that can be used is a line-of-sight detection method based on a Purkinje image obtained by reflecting irradiated light off the cornea. More precisely, a line-of-sight detection method based on the pupil center-corner reflection method is performed. The pupil center-corner reflection method is used to calculate a line-of-sight vector that expresses the orientation (rotation angle) of the eyeball based on a pupil image and a Purkinje image contained within the captured eyeball image, thereby capturing the user's line of sight. In this embodiment, the display device can include a photoelectric conversion device containing a photoelectric conversion element, and can control the display image of the display device based on line-of-sight information from the user to the photoelectric conversion device. Specifically, based on the line-of-sight information, the display device sets a first field of view, which the user is looking at, and a second field of view that differs from the first. The first and second fields of view can be set by a control device within the display device, or the set field of view can be received from an external control device. The display device's display range can be controlled such that the display resolution in the first field of view is higher than the display resolution in the second field of view. In other words, the resolution in the second field of view can be lower than that in the first field of view. Furthermore, the display area can include a primary display area and a secondary display area that differs from the primary display area. Based on line-of-sight information, a high-priority area can be selected from the primary and secondary display areas. The primary and secondary display areas can be set by the display device's control unit, or the set display areas can be received from an external control unit. The resolution in the high-priority area can be controlled to be higher than the resolution in any area other than the high-priority area. In other words, the resolution in an area with a relatively low priority level can be reduced. Artificial intelligence (AI) can be used to set the first field of view or the high-priority area. The AI ​​can be a model that uses an image of an eyeball and the actual gaze direction of the eyeball within the image as training data to estimate the angle of the line of sight and the distance to a visual target from the image of the eyeball. An AI program can be contained within the display device, the photoelectric conversion device, or an external device. If the AI ​​program is contained within the external device, it is transmitted to the display device via communication. If the display control is to be based on visibility detection, the embodiment can be applied to smart glasses, which further include a photoelectric conversion device that captures an external image. The smart glasses can display the captured external image information in real time. The embodiments described above can be modified appropriately without deviating from the technical concept. An example obtained by adding a partial configuration from one embodiment to another, or an example obtained by replacing a partial configuration with that of another embodiment, is also included in the embodiments of the present invention. The embodiments according to the invention include the following configurations and methods. Configuration 1Photoelectric conversion device comprising: a photoelectric conversion element configured to receive a photon; an exposure control device configured to generate a signal defining a plurality of second exposure periods contained within a first exposure period corresponding to a frame, each second exposure period being shorter than the first exposure period; a timing generator device configured to generate a pulse signal defining timing information within each second exposure period; a measuring device configured to count the pulse signal at or after a first photon detection in the second exposure period based on the pulse signal generated by the timing generator device;and a pulse control device configured to perform a counting control of the pulse signal in a second exposure period following the second exposure period based on a value from the measuring device, wherein the subsequent second exposure period is one from the plurality of second exposure periods. Configuration 2 Photoelectric conversion device according to configuration 1, wherein the pulse control device performs the counting control of the pulse signal in the subsequent second exposure period by selecting the pulse signal from a plurality of pulse signals. Configuration 3 Photoelectric conversion device according to configuration 1 or 2, wherein, if the value of the measuring device is less than a predetermined value, the pulse signal in the subsequent second exposure period is increased in number relative to the pulse signal in the second exposure period. Configuration 4 Photoelectric conversion device according to one of configurations 1 to 3, wherein, if the value of the measuring device is greater than a predetermined value, the number of pulse signals in the subsequent second exposure period is reduced relative to the pulse signal in the second exposure period. Configuration 5 Photoelectric conversion device according to one of configurations 1 to 4, wherein the timing generator device generates the pulse signal with a uniform interval, and wherein the pulse signal is input into the measuring device at least in the second exposure period. Configuration 6 Photoelectric conversion device according to one of configurations 1 to 4, wherein the timing generator device generates the pulse signal with a non-uniform interval, and wherein the pulse signal is input into the measuring device at least in the second exposure period. Configuration 7 Photoelectric conversion device according to configuration 6, wherein the pulse signal with the non-uniform interval is arranged such that one period of it increases in accordance with an elapsed time in the second exposure period. Configuration 8 Photoelectric conversion device according to configuration 6 or 7, wherein the pulse signal with the non-uniform interval has an interval that is set to a logarithmic compression of real time. Configuration 9 Photoelectric conversion device according to one of configurations 1 to 8, further comprising: a correction circuit configured to correct a signal output by the measuring device, wherein the correction circuit modifies a correction method based on a count value of the pulse signal. Configuration 10 Photoelectric conversion device according to configuration 9, wherein, if the pulse signal in the subsequent second exposure period is reduced in number relative to the pulse signal in the second exposure period, the correction circuit changes the value output by the measuring device to a larger value. Configuration 11 Photoelectric conversion device according to one of configurations 1 to 10, wherein the measuring device includes a waveform shaping circuit that converts a signal from the photoelectric conversion element into a pulse signal. Configuration 12 Photoelectric conversion device according to one of configurations 1 to 11, wherein the measuring device includes a timing determination circuit, wherein the timing determination circuit outputs the pulse signal generated by the timing generator device at or after a time of first photon detection within the second exposure period. Configuration 13 Photoelectric conversion device according to configuration 12, wherein the measuring device includes a counter circuit, wherein the counter circuit receives a count value by performing a count for each input of the pulse signal output by the timing determination circuit within the second exposure period. Configuration 14 Photoelectric conversion device according to configuration 13, wherein the counter circuit obtains a total value by adding up the count values ​​from the multitude of second exposure periods and outputs the total value. Configuration 15 Photoelectric conversion device according to one of the configurations 1 to 14, wherein the photoelectric conversion element is an avalanche photodiode. Configuration 16 Photoelectric conversion device according to configuration 15, wherein a switch configured to perform a charging process is located between the avalanche photodiode and a power supply. Configuration 17 Photoelectric conversion device according to configuration 16, wherein every second exposure period is a period from a time at which the charging process is carried out to a time at which the charging process is subsequently carried out. Configuration 18 Photoelectric conversion device according to one of configurations 1 to 13, wherein the measuring device includes a selection circuit, and wherein the plurality of second exposure periods includes a first of the second exposure periods and a second of the second exposure periods, and wherein the selection circuit selects whether or not to output a signal corresponding to the pulse signal that defines the time information within the second of the second exposure periods between the time at which the photon is not detected in the first of the second exposure periods and the time at which the photon is detected in the first of the second exposure periods. Configuration 19 Photoelectric conversion device according to configuration 18, wherein, if the photon is not detected in the first of the second exposure periods, the selection circuit outputs a predetermined value, regardless of a time period from the beginning of the second of the second exposure periods until the first photon detection. Configuration 20 Photoelectric conversion device according to one of configurations 1 to 19, wherein a first substrate and a second substrate are stacked, wherein the first substrate includes the photoelectric conversion element, and wherein the second substrate includes the exposure control device, the timing generator device, the measuring device and the pulse control device. Configuration 21 Photoelectric conversion device according to configuration 7, wherein a first substrate, a second substrate and a third substrate are stacked, wherein the first substrate includes the photoelectric conversion element, wherein the second substrate includes the waveform shaping circuit, the timing determination circuit, the counter circuit and the pulse control device, and wherein the third substrate includes a second timing determination circuit, a second counter circuit and a second pulse control device. Configuration 22 Photoelectric conversion device according to configuration 21, wherein a pulse signal generated by the timing generator device and to be input into the timing determination circuit contained in the second substrate is different from a pulse signal generated by the timing generator device and to be input into the second timing determination circuit contained in the third substrate. Configuration 23 Photoelectric conversion system comprising: the photoelectric conversion device according to one of configurations 1 to 22; and a signal processor configured to produce an image using a signal output by the photoelectric conversion device. Configuration 24 Mobile object comprising: the photoelectric conversion device according to one of configurations 1 to 22; and a control device configured to control a movement of the mobile object using a signal output by the photoelectric conversion device. According to the present invention, a larger amount of signal information can be acquired, compared to the international PCT publication with the number WO 2020 / 179928. Although the present invention is described with reference to exemplary embodiments, it is not limited to the disclosed embodiments. The scope of the following claims is to be interpreted as broadly as possible to encompass all such modifications and equivalent structures and functions. QUOTES INCLUDED IN THE DESCRIPTION This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature WO 2020 / 179928 [0002, 0003, 0187]

Claims

Photoelectric conversion device comprising: a photoelectric conversion element configured to receive a photon; an exposure control device configured to generate a signal defining a plurality of second exposure periods contained within a first exposure period corresponding to a frame, each second exposure period being shorter than the first exposure period; a timing generator device configured to generate a pulse signal defining timing information within each second exposure period; a measuring device configured to count the pulse signal at or after a first photon detection in the second exposure period based on the pulse signal generated by the timing generator device;and a pulse control device configured to perform a counting control of the pulse signal in a second exposure period following the second exposure period based on a value from the measuring device, wherein the subsequent second exposure period is one from the plurality of second exposure periods. Photoelectric conversion device according to claim 1, wherein the pulse control device performs the counting control of the pulse signal in the subsequent second exposure period by selecting the pulse signal from a plurality of pulse signals. Photoelectric conversion device according to claim 1 or 2, wherein, if the value of the measuring device is less than a predetermined value, the number of pulse signals in the subsequent second exposure period is increased relative to the pulse signal in the second exposure period. Photoelectric conversion device according to one of claims 1 to 3, wherein, if the value of the measuring device is greater than a predetermined value, the number of pulse signals in the subsequent second exposure period is reduced relative to the pulse signal in the second exposure period. Photoelectric conversion device according to one of claims 1 to 4, wherein the timing generator device generates the pulse signal with a uniform interval, and wherein the pulse signal is input into the measuring device at least in the second exposure period. Photoelectric conversion device according to one of claims 1 to 4, wherein the timing generator device generates the pulse signal with a non-uniform interval, and wherein the pulse signal is input into the measuring device at least in the second exposure period. Photoelectric conversion device according to claim 6, wherein the pulse signal with the non-uniform interval is configured such that one period of it increases in accordance with an elapsed time in the second exposure period. Photoelectric conversion device according to claim 6 or 7, wherein the pulse signal with the non-uniform interval has an interval that is set to a logarithmic compression of real time. Photoelectric conversion device according to any one of claims 1 to 8, further comprising: a correction circuit configured to correct a signal output by the measuring device, wherein the correction circuit modifies a correction method based on a count value of the pulse signal. Photoelectric conversion device according to claim 4, further comprising: a correction circuit configured to correct a signal output by the measuring device, wherein, if the number of pulses in the subsequent second exposure period is reduced relative to the pulse signal in the second exposure period, the correction circuit changes the value output by the measuring device to a larger value. Photoelectric conversion device according to any one of claims 1 to 10, wherein the measuring device comprises a waveform shaping circuit which converts a signal from the photoelectric conversion element into a pulse signal, a timing determination circuit and a counter circuit, wherein the timing determination circuit outputs the pulse signal generated by the timing generator device at or after a time of first photon detection within the second exposure period; and wherein the counter circuit obtains a count value by performing a count for each input of the pulse signal output by the timing determination circuit within the second exposure period. Photoelectric conversion device according to claim 11, wherein the counter circuit obtains a total value by adding up the count values ​​from the plurality of second exposure periods and outputs the total value. Photoelectric conversion device according to one of claims 1 to 12, wherein the photoelectric conversion element is an avalanche photodiode. Photoelectric conversion device according to claim 13, wherein a switch configured to perform a charging process is arranged between the avalanche photodiode and a power supply that applies a reverse bias to the avalanche photodiode, and wherein every second exposure period is a period from a time at which the charging process is performed to a time at which the charging process is subsequently performed. Photoelectric conversion device according to one of claims 1 to 14, wherein the measuring device includes a selection circuit, and wherein the plurality of second exposure periods includes a first of the second exposure periods and a second of the second exposure periods, and wherein the selection circuit selects whether or not to output a signal corresponding to the pulse signal that defines the time information within the second of the second exposure periods between the time at which the photon is not detected in the first of the second exposure periods and the time at which the photon is detected in the first of the second exposure periods. Photoelectric conversion device according to claim 15, wherein, if the photon is not detected in the first of the second exposure periods, the selection circuit outputs a predetermined value, irrespective of a time period from the start of the second of the second exposure periods until the first photon detection. Photoelectric conversion device according to one of claims 1 to 16, wherein a first substrate and a second substrate are stacked, wherein the first substrate includes the photoelectric conversion element, and wherein the second substrate includes the exposure control device, the timing generator device, the measuring device and the pulse control device. Photoelectric conversion device according to claim 11, wherein a first substrate, a second substrate and a third substrate are stacked, wherein the first substrate includes the photoelectric conversion element, wherein the second substrate includes the waveform shaping circuit, the timing determination circuit, the counter circuit and the pulse control device, and wherein the third substrate includes a second timing determination circuit, a second counter circuit and a second pulse control device. Photoelectric conversion device according to claim 18, wherein a pulse signal generated by the timing generator device and intended to be input into the timing determination circuit contained in the second substrate is different from a pulse signal generated by the timing generator device and intended to be input into the second timing determination circuit contained in the third substrate. Photoelectric conversion system comprising: the photoelectric conversion device according to any one of claims 1 to 19; and a signal processor configured to generate an image using a signal output by the photoelectric conversion device.

Images