SPAD-based image sensor and method for operating same

Abstract

Provided are an image sensor, and a method for operating same, the image sensor comprising a pixel array having a plurality of pixels, each pixel comprising: a SPAD for sensing photons and generating impulse signals; a counter for counting the number of pulse signals; a multiplexer for selecting, in accordance with a mode selection signal, one count bit cell among a plurality of count bit cells of the counter, and outputting an overflow signal based on the bit value of the selected count bit cell; and a front-end module for converting the impulse signals to pulse signals, and when the overflow signal is issued, converting global clock signals to pulse signals and transmitting to the counter. As such, light can be sensed with ultra-high precision at low power, and by varying the period to which extrapolation is applied, light can be sensed with adjustments to the level of precision.

Description

SPAD-based image sensor and its operating method

[0001] The present disclosure relates to an image sensor and an operating method thereof, and more particularly, to a SPAD-based image sensor and an operating method thereof.

[0002] An image sensor is a device that detects incident light and converts it into an electrical signal to create an image. It may include various sensing elements capable of detecting light. Conventional optical sensing elements have mainly used CMOS elements or CCD elements. However, due to the increasing demand for ultra-sensitive optical sensors, single photon avalanche diodes (SPADs), which can directly detect a single photon, the smallest unit of light, have been developed recently, and research on image sensors using SPAD elements is actively underway.

[0003] The SPAD device can detect light with ultra-high sensitivity by applying a reverse bias voltage higher than the breakdown voltage, so that it can be triggered by even a single photon and cause an avalanche breakdown phenomenon. When the SPAD device detects a photon and an avalanche breakdown phenomenon occurs, a large current temporarily flows, outputting a signal in the form of an impulse waveform. After outputting the impulse signal, the SPAD device quenches and returns to its previous state. Accordingly, a SPAD-based image sensor detects the intensity of the incident light by counting the number of impulse signals output from the SPAD device equipped in each pixel and acquires an image. In other words, if many photons are incident and the number of counted impulse signals is large, a bright image is acquired, and if the number of counted impulse signals is small, a dark image is acquired.

[0004] In a SPAD-based image sensor, each pixel is equipped with a SPAD element and a counter for counting the number of impulse signals generated from the SPAD element, where the count range and bit number of the counter are determined in advance depending on the intended use of the image sensor.

[0005] In these SPAD-based image sensors, the SPAD element operates by utilizing the avalanche breakdown phenomenon induced by the application of a high-voltage reverse bias voltage as described above, which results in large power consumption each time an impulse signal is generated. In other words, there is a problem that very large power consumption occurs when detecting a bright image in which impulse signals are repeatedly generated a large number of times.

[0006] Moreover, image sensors must be able to detect light intensity across a wide range of different application areas. However, conventional SPAD-based image sensors have a fixed counter bit count. This requires individual image sensors with counters of different bit counts for different applications, leading to increased manufacturing costs.

[0007] The purpose of the present disclosure is to provide an image sensor capable of detecting light with ultra-high precision while reducing power consumption, and an operating method thereof.

[0008] The purpose of the present disclosure is to provide an image sensor capable of detecting light while adjusting precision according to the intended use, and an operating method thereof.

[0009] The image sensor of the present disclosure and its operating method can estimate the number of impulse signals generated from a SPAD element based on an extrapolation method without continuously counting them during the exposure time, thereby reducing the operating time of the SPAD element, thereby enabling ultra-high-precision light detection with low power consumption. Furthermore, by varying the section to which the extrapolation method is applied depending on the intended use, light can be detected with controlled precision.

[0010] Figure 1 shows a schematic configuration of a SPAD-based image sensor.

[0011] Figure 2 shows a schematic configuration of the pixels of Figure 1.

[0012] Figure 3 shows a schematic configuration of a pixel according to one embodiment.

[0013] FIG. 4 is a drawing for explaining an extrapolation method applied to a SPAD-based image sensor having the pixels of FIG. 3.

[0014] Fig. 5 shows a schematic configuration of a pixel according to another embodiment.

[0015] FIG. 6 illustrates an operation method of a SPAD-based image sensor according to one embodiment.

[0016] According to one embodiment of the present disclosure, an image sensor includes a pixel array including a plurality of pixels, each of the plurality of pixels including a SPAD for detecting a photon and generating an impulse signal; a counter for counting the number of pulse signals applied; a multiplexer for selecting one of a plurality of count bit cells of the counter according to a mode selection signal and outputting an overflow signal according to a bit value of the selected count bit cell; and a front-end module for converting the impulse signal into the pulse signal and, when the overflow signal is applied, converting a global clock signal into the pulse signal and transmitting the pulse signal to the counter.

[0017] The above shear module can drive the SPAD during a light detection operation, and stop driving the SPAD when the overflow signal is applied.

[0018] The above-mentioned shear module can convert the impulse signal or the global clock signal applied until the exposure time set during the light detection operation into the pulse signal and transmit it to the counter.

[0019] The above shear module can receive the global clock signal by responding to the overflow signal once until the set exposure time.

[0020] The above shear module can initialize the counter after a set exposure time.

[0021] The above multiplexer may be implemented as included in one of the front-end modules or the counter.

[0022] The image sensor further includes a control module, and the control module can generate the mode selection signal and, after a set exposure time, receive a count value from the counter to obtain a pixel value.

[0023] The above control module can obtain the overflow count and overflow time from the count value according to the count bit cell of the counter selected according to the mode selection signal, and can obtain the pixel value by calculating it according to the extrapolation method based on the obtained overflow count and overflow time and the exposure time.

[0024] The above control module selects one of a plurality of timing gain tables in which pixel values ​​according to count values ​​are calculated and stored in advance, according to a selected count bit cell, and then searches for a pixel value corresponding to the count value in the selected timing gain table to obtain the pixel value.

[0025] The above control module can generate the mode selection signal by independently setting a count bit cell selected from each of the plurality of pixels.

[0026] According to another embodiment of the present disclosure, a method of operating an image sensor includes a pixel array composed of a plurality of pixels, each pixel having a SPAD and a counter, and a control module, the method comprising: generating a mode selection signal for selecting one count bit cell from among a plurality of count bit cells of the counter to output an overflow signal; counting the number of impulse signals generated according to a photon detected by driving the SPAD; generating an overflow signal in response to a bit value of a count bit cell selected in the counter according to the mode selection signal; and counting a global clock signal when the overflow signal is generated.

[0027] Hereinafter, specific embodiments according to the present disclosure will be described with reference to the drawings. The following detailed description is provided to facilitate a comprehensive understanding of the methods, devices, and / or systems described herein. However, these are merely examples and the present invention is not limited thereto.

[0028] In describing embodiments of the present disclosure, if a detailed description of a known technology related to the present invention is judged to unnecessarily obscure the gist of the embodiments, the detailed description will be omitted. In addition, the terms described below are terms defined in consideration of their functions in the present invention, and this may vary depending on the intention or custom of the user or operator. Therefore, the definitions should be made based on the contents throughout this specification. The terminology used in the detailed description is only for the purpose of describing one embodiment and should never be limited. Unless clearly used otherwise, the singular form includes the plural form. In this description, expressions such as “comprises” or “comprising” are intended to indicate certain features, numbers, steps, operations, elements, parts or combinations thereof, and should not be construed to exclude the presence or possibility of one or more other features, numbers, steps, operations, elements, parts or combinations thereof other than those described. Additionally, terms such as “...unit,” “...device,” “module,” and “block” described in the specification mean a unit that processes at least one function or operation, which may be implemented by hardware, software, or a combination of hardware and software.

[0029] Fig. 1 shows a schematic configuration of a SPAD-based image sensor, and Fig. 2 shows a schematic configuration of a pixel of Fig. 1.

[0030] Referring to FIG. 1, a SPAD-based image sensor includes a pixel array (10) and a control module (20). The pixel array (10) includes a plurality of pixels (px) arranged in an array, and may include pixels (px) arranged in an array of M × N, for example. FIG. 2 shows an example of a configuration for one pixel (30) among the plurality of pixels (px) of the pixel array (10) of FIG. 1.

[0031] The pixel (30) illustrated in FIG. 2 can be configured to include a SPAD (31), a shear module (32), and a counter (33).

[0032] SPAD(31) has a reverse bias voltage (V) greater than the breakdown voltage SPAD ) (e.g., 23 V) can be applied and implemented as an avalanche diode operating in Geiger Mode. The SPAD (31) can generate an impulse signal by reacting to photons with high sensitivity and causing an avalanche breakdown phenomenon.

[0033] The shear module (32) controls the operation of the SPAD (31) according to the control of the control module (20), and can convert the impulse signal output from the driven SPAD (31) into a pulse signal and transmit it to the counter (33).

[0034] For example, the shear module (32) can prevent the SPAD (31) from being driven by applying a certain level of driving control voltage to the anode terminal of the SPAD (31) under the control of the control module (20) so that the voltage difference between the two ends of the SPAD (31) becomes lower than the breakdown voltage, but the method of controlling the driving of the SPAD (31) can be changed in various ways.

[0035] In addition, the front module (32) can level-shift the pulse signal to have a lower voltage level than the impulse signal and transmit it to the counter (33). As described above, in the SPAD (31), a reverse bias voltage (V) of high voltage (e.g., 23 V) SPAD ) is applied and a photon is incident, causing an avalanche breakdown phenomenon, a high-voltage impulse signal may be generated. To prevent such an impulse signal from being transmitted to the counter (33) as is, the front module (32) can level-shift the applied high-voltage impulse signal to a low-voltage level (e.g., 3 V) and convert it into a pulse signal to transmit it to the counter (33).

[0036] Additionally, the shear module (32) can cause the SPAD (31) in which the avalanche breakdown phenomenon has occurred to be quickly quenched and returned to its previous state, and can reset the counter (33) to initialize the pixel value counted by the counter (33).

[0037] The front module (32) may include a plurality of switches implemented with transistors, a plurality of logic elements, and a level shift circuit; however, the components and circuit configurations constituting the front module (32) may be designed in various ways, and thus a detailed description thereof is omitted here.

[0038] The counter (33) counts the number of pulse signals applied from the front module (32) and obtains a pixel value that measures the amount of light (or intensity of light) incident on the pixel (30). At this time, the counter (33) can be implemented as an N-bit counter, and the number of bits (N) of the counter (33) is preset according to the intended use of the image sensor.

[0039] The control module (20) controls the front module (32) of each of the plurality of pixels (px) of the pixel array (10) to control the operation of the SPAD (31) included in each pixel (px). For example, the control module (20) can enable a plurality of pixels (px) of the pixel array (10) to detect light simultaneously, or to detect pixels in units of rows or columns. In some cases, only some of the plurality of pixels (px) of the pixel array (10) can be selectively enabled to detect light according to various combinations. In addition, the control module (20) can control the front module (32) to adjust the exposure time, which represents the time for each of the plurality of pixels (px) to detect photons.

[0040] In addition, the control module (20) can receive pixel values ​​transmitted from the counter (33) for each pixel and configure an image. That is, the control module (20) can not only operate as a control circuit that controls the pixel array (10), but also operate as an image processing circuit.

[0041] SPAD (31), shear module (32), and counter (33) may all be implemented on the same layer, but in some cases, SPAD (31), shear module (32), and counter (33) may be implemented on different layers.

[0042] In the case of the pixel shown in Fig. 2, since the number of bits (N) of the counter (33) is preset and fixed, the range of pixel values ​​that can be output from each pixel (30) is 0 to 2. N It's -1.

[0043] Therefore, the number of impulse signals generated by SPAD (31) in each of the plurality of pixels (30) until the exposure time is not limited, but the counter (33) can generate up to 2 N -1 impulse signal can be counted. Accordingly, the front module (32) counts the value counted in the counter (33) as the maximum value (2 N -1) When SPAD (31) is reached, power consumption can be reduced by preventing it from being driven.

[0044] Figure 3 shows a schematic configuration of a pixel according to one embodiment.

[0045] FIG. 3 also shows an example of the configuration of each of a plurality of pixels (px) provided in the pixel array (10) in the image sensor illustrated in FIG. 1. The pixel (40) of FIG. 3 may also include a SPAD (41), a front module (42), and a counter (43), similar to that in FIG. 2.

[0046] Here, SPAD (41) has the same configuration as SPAD (31) of Fig. 2 and is not described further. However, the front module (42) and the counter (43) may be configured differently from the front module (32) and the counter (33) of Fig. 2. Specifically, the counter (43) may be implemented as a fixed N-bit counter, basically like the counter (33) of Fig. 2. However, in Fig. 3, the counter (43) may transmit an overflow signal (OF) to the front module (42) when the counted value according to the applied pulse signal is greater than or equal to a designated reference value. Here, as an example, it is assumed that the counter (43) transmits an overflow signal (OF) to the front module (42) according to the bit value of the Most Significant Bit (MSB). That is, when the counted value in the N-bit counter (43) is 2 N-1 When this becomes 1 and the MSB becomes 1, an overflow signal (OF) can be output to the front module (42). However, the bit position at which the overflow signal (OF) is output can be set to a different position in advance depending on the intended use.

[0047] And the front module (42) prevents the SPAD (41) from being driven when an overflow signal (OF) is applied from the counter (43). Therefore, the SPAD (41) no longer generates an impulse signal. However, the front module (42) generates a global clock signal ( ) is authorized, and the authorized global clock signal ( ) can transmit a pulse signal to the counter (33). That is, when the overflow signal (OF) is applied to the front module front module (42), the global clock signal (not the impulse signal) is transmitted. ) can be used to generate a pulse signal and transmit it to the counter (43).

[0048] Accordingly, the counter (43) counts the number of pulse signals generated according to the impulse signal generated from SPAD (41), and then continuously generates a global clock signal ( ) counts the number of pulse signals generated. 2 N An N-bit counter (43) that can count values ​​up to -1 generates 2 pulses according to the impulse signal. N-1 Since only the values ​​up to 2 are counted, the counter (43) counts the remaining 2 N-1 +1 ~ 2 N For the range of -1, the global clock signal ( ) can count the number of pulses.

[0049] And the shear module (42) controls the exposure time (T) according to the control of the control module (20). EXP ) to the global clock signal ( ) transmits a pulse signal to the counter (43).

[0050] FIG. 4 is a drawing for explaining an extrapolation method applied to a SPAD-based image sensor having the pixels of FIG. 3.

[0051] When a plurality of pixels (px) of the pixel array (10) are composed of pixels (30) of FIG. 2, each pixel (30) has a preset exposure time (T) under the control of the control module (20). EXP ) and count the number of photons incident during the pixel value (N PH ) is obtained.

[0052] Here the exposure time (T EXP ) is already set, and at each pixel (px) the photon is exposed for an exposure time (T EXP ) can be considered to be uniformly incident during the exposure time (T). Therefore, as shown in Fig. 4, the exposure time (T EXP ) does not count all the incident photons, but the number of incident photons is a certain number (here, the overflow number (N) as an example). OF )) is the overflow time (T OF ) is known, the exposure time (T) can be estimated using a simple proportional equation by extrapolation. EXP) the number of photons incident during the period, i.e. pixel value (N PH ) can be easily estimated.

[0053] Referring to Figure 4, the pixel values ​​(N) according to the extrapolation method PH ) can be calculated as in mathematical formula 1.

[0054]

[0055] The number of overflows in mathematical expression 1 (N) OF ) and exposure time (T EXP ) is already set, so the overflow time (T OF ) can be checked, the pixel value (N PH ) can be easily calculated.

[0056] And in the pixel (40) structure of Fig. 3, the overflow time (T OF ) is the time when the overflow signal (OF) is generated. However, the global clock signal ( ) is used to generate an overflow signal (OF) at the overflow time (T OF ) to directly measure the global clock signal ( in addition to the counter (43) for counting the number of pulse signals according to the impulse signal. ) requires an additional separate counter to count the number of exposure times (T EXP ) is preset, so the overflow time (T) at which the overflow signal (OF) is generated OF ) after exposure time (T EXP ) to the global clock signal ( ) using the measurement (T MEA ) and exposure time (T EXP ) measured in time (T MEA ) deducted (T EXP - T MEA ), then the overflow time (T OF ) can be easily calculated.

[0057] And as mentioned above, in the pixel (40) shown in Fig. 3, the counter (43) has an overflow count (N OF ) 2 N-1 Since it is assumed that only the values ​​up to are counted according to the impulse signal, the following 2 N-1 +1 ~ 2 N -1 global clock signal within the range ) can count the number of pulses according to the overflow time (T). That is, the counter (43) provided to count the number of impulse signals OF ) after which the measurement time (T MEA ) to determine the global clock signal ( ) can be recycled to count the number of clocks. Therefore, the extrapolation method can be applied to one counter (43) to obtain the pixel value (N PH ) can be estimated.

[0058] Pixel value (N PH ) can be estimated by the control module (20) that receives the count value counted by the counter (43). Here, since it is assumed that the counter (43) outputs an overflow signal (OF) according to the bit value of the MSB, the control module (20) outputs a global clock signal () counted from the bit values ​​excluding the MSB among the bit values ​​output from the counter (43). ) can be checked. And the global clock signal ( ) from the number of overflow times (T OF ) can be estimated, and the estimated overflow time (T OF ) into mathematical equation 1, the pixel value (N PH ) can be obtained. However, for each of the plurality of pixels (px) provided in the pixel array (10), a pixel value (N PH ) is inefficient because it requires a lot of computation. Therefore, the control module (20) calculates the pixel value (N) according to the count value. PH) is used to calculate pixel values ​​(N) using a timing gain table that is calculated and stored in advance. PH ) can be obtained immediately, thereby greatly reducing the amount of computation.

[0059] In the pixel (40) of Fig. 4, the shear module (42) has an overflow time (T OF ) after exposure time (T EXP ) so that the SPAD (41) is not driven, the power consumption of the pixel array (10) can be significantly reduced.

[0060] Fig. 5 shows a schematic configuration of a pixel according to another embodiment.

[0061] The pixel (50) in FIG. 5 may also include a SPAD (51), a shear module (52), and a counter (53), basically like the pixel (40) in FIG. 4. The SPAD (51) and the shear module (52) may operate in the same manner as the SPAD (41) and the shear module (42) provided in the pixel (40) in FIG. 4.

[0062] That is, the SPAD (51) is driven according to the control of the front module (52) and outputs an impulse signal due to the avalanche breakdown phenomenon when a photon is detected. The front module (52) controls the driving of the SPAD (51), converts the impulse signal applied from the SPAD (51) into a pulse signal and transmits it to the counter (53). In addition, when an overflow signal (OF) is applied from the counter (53), the SPAD (51) is not driven and the exposure time (T EXP ) to the global clock signal ( ) is authorized to receive a global clock signal ( ) transmits a pulse signal to the counter (53).

[0063] The counter (43) is implemented as an N-bit counter capable of counting N-bit values, similar to the counters (33, 43) of FIGS. 2 and 4, and can count the number of pulse signals transmitted from the front module (52). Then, the counter (43) outputs an overflow signal (OF) to the front module (52) according to the counted value. However, the counter (53) of FIG. 5 does not output the overflow signal (OF) solely based on the bit value of a specific bit (e.g., MSB) set in advance, but outputs the overflow signal (OF) according to the bit value of the bit specified by the mode selection signal (sel).

[0064] To this end, the counter (53) further includes a multiplexer (54) that receives a mode selection signal (sel), as illustrated in Fig. 5. The multiplexer (54) is connected to designated count bit cells among a plurality of count bit cells in which bit values ​​are each stored in the counter (53), receives a bit value, and selects a bit value of a specific count bit cell according to the mode selection signal (sel) to output an overflow signal (OF).

[0065] In Fig. 5, as an example, a case is illustrated in which a multiplexer (54) selects one of the bit values ​​of the k + m-th bit, the k-th bit, and the km-th bit according to a mode selection signal (sel), and outputs an overflow signal (OF) according to the selected bit value. Here, the k + m-th bit may be the MSB of an N(= k + m)-bit counter (53), and when the multiplexer (54) selects the k + m-th bit according to the mode selection signal (sel), the pixel of Fig. 5 may operate in the same manner as the pixel of Fig. 4.

[0066] However, the multiplexer (54) can output an overflow signal (OF) by selecting the k-th bit or the km-th bit according to the mode selection signal (sel). That is, the counter (53) in Fig. 5 can operate similarly to a variable bit counter in which the count value that outputs the overflow signal (OF) is adjusted according to the mode selection signal (sel).

[0067] Therefore, the counter (53) has an overflow time (T OF ) can be adjusted. And when the number of impulse signals that can be counted is adjusted, the measurement time (T) to which the extrapolation method is applied is adjusted. MEA ) a global clock signal that can be measured during ) can be adjusted. As described above, in the pixel structure of FIGS. 4 and 5, a single counter (43, 53) is used to control the overflow time (T OF ) as well as the number of impulse signals up to the global clock signal ( ) is configured to be counted together.

[0068] When the number of impulse signals that can be counted is adjusted, the global clock signal that can be counted ( ) can be adjusted together. For example, if the number of impulse signals that can be counted by the multiplexer (54) is reduced by selecting the km-th bit from the previously set k-th bit by the mode selection signal (sel), the overflow time (T) for directly counting the number of input photons OF ) is shortened, while the global clock signal ( ) to which the extrapolation method is applied. The measurement time (T) MEA ) increases. In this case, the power consumption of the SPAD (51) can be further reduced compared to the pixel of Fig. 4 that simply applies the extrapolation method, but the accuracy may be lowered.

[0069] When the number of impulse signals that the multiplexer (54) can count by selecting the k+mth bit by the mode selection signal (sel) increases, the overflow time (T OF ) increases, and the measurement time (T MEA ) becomes shorter. In this case, the power consumption of SPAD (51) increases, but the accuracy can be improved.

[0070] Therefore, depending on the intended use, the overflow time (T OF ) can be used to trade off power consumption and accuracy. When using a variable bit counter, the range that the counter can count changes, so the overflow time (T OF ) and measurement time (T MEA ) increases or decreases together, causing the power consumption and accuracy to increase or decrease together, whereas, as in Fig. 5, if the bit at which the overflow signal (OF) is output is configured to be selected, the entire countable range of the counter is maintained as is, allowing the level of power consumption and accuracy to be adjusted.

[0071] Here, the multiplexer (54) is described as being provided within the counter (53), but the multiplexer (54) may be provided in the front module (52) or may be configured separately from the counter (53) or the front module (52).

[0072] And if the bit that outputs the overflow signal (OF) is not the MSB, the bit value of the corresponding bit may change again as the count value of the counter (53) increases, and the state of the overflow signal (OF) may change, but this is because the front module (52) has an exposure time (T EXP ) can be simply solved by configuring it to respond to the overflow signal (OF) only once during the exposure time (T). The front module (52) has an exposure time (T EXP) After the counter (53) is initialized, it can be reset to respond again to the overflow signal (OF).

[0073] The control module (20) applies a mode selection signal (sel) to the multiplexer (54). And according to mathematical expression 1, the pixel value (N PH ) is calculated, but the overflow time (T) is adjusted according to the mode selection signal (sel). OF ) and measurement time (T MEA ) considering the pixel value (N PH ) can be calculated in different ways. However, the pixel value (N) according to the count value PH ) is provided with a plurality of timing gain tables that are calculated and stored in advance, and one of the plurality of timing gain tables is selected according to the mode selection signal (sel), and then the pixel value (N) corresponding to the count value of the counter (53) is PH ) can also be obtained by exploring.

[0074] In some cases, the control module (20) may select the upper bit (e.g., the k+mth bit) of the counter (53) by the mode selection signal (sel) for some pixels (e.g., the pixels of the area of ​​interest) among the plurality of pixels (px) of the pixel array (10) to improve accuracy, while reducing power consumption by selecting the upper bit (e.g., the kmth bit) for the remaining pixels, thereby balancing power consumption and accuracy for the entire pixel array (10).

[0075] As a result, the SPAD-based image sensor of the present disclosure is configured to output an overflow signal (OF) according to the bit value of a count bit cell selected by varying it according to a mode selection signal (sel) among a plurality of count bit cells of a counter (53) provided in each pixel (px), thereby allowing power consumption to be reduced or accuracy to be improved depending on the intended use separately.

[0076] In the illustrated embodiment, each component may have different functions and capabilities beyond those described below, and may include additional components beyond those described below. Furthermore, in one embodiment, each component may be implemented using one or more physically separate devices, or may be implemented by one or more processors, or a combination of one or more processors and software, and, unlike the illustrated example, may not be clearly distinguished in their specific operations.

[0077] FIG. 6 illustrates an operation method of a SPAD-based image sensor according to one embodiment.

[0078] In Fig. 6, the operation of the image sensor of Fig. 1 is explained based on the pixel configuration of Fig. 5. Referring to Fig. 6, the control module (20) first sets a count bit cell that outputs an overflow signal (OF) among a plurality of count bit cells of a counter (53) provided in each of a plurality of pixels (px) of the pixel array (10), and generates a mode selection signal (sel) according to the set count bit cell and transmits it to each pixel (px) (S110). Here, the control module (20) may be set identically for all pixels (px) of the pixel array (10), but may be set differently for each pixel.

[0079] Each pixel (px) can be configured to include a SPAD (51), a front module (52), a counter (53), and a multiplexer (54), and the multiplexer (54) of the pixel (px) to which the mode selection signal (sel) is applied selects a count bit cell according to the mode selection signal (sel) among a plurality of count bit cells of the counter (53).

[0080] And the SPAD (51) provided in each of the plurality of pixels (px) of the pixel array (10) is driven (S120). The control module (20) can drive the SPAD (51) by controlling the front module (52). At this time, the control module (20) can control all pixels (px) of the pixel array (10) to be driven simultaneously, or can control them to be driven at different times.

[0081] The driven SPAD (51) repeatedly generates an impulse signal in response to an incident photon, and the front module (52) converts the impulse signal generated from the SPAD (51) into a pulse signal and transmits it to the counter (53), and the counter (53) counts the number of applied pulses (S130). As the counter (53) counts the number of pulses, the bit value starts to change from the lower count bit cell among the plurality of count bit cells, and when the bit value of the set counter bit cell changes, the multiplexer (54) transmits an overflow signal (OF) to the front module.

[0082] Accordingly, the front module (52) determines whether an overflow signal (OF) is generated (S140). If the overflow signal (OF) is not generated, the front module (52) continues to drive the SPAD (51), converts the impulse signal generated from the SPAD (51) into a pulse signal, and the counter (53) continuously counts the number of pulses (S120, S130).

[0083] However, when an overflow signal (OF) occurs, the front module (52) stops driving the SPAD (51) and the global clock signal ( ) is applied to generate a pulse signal and transmits it to the counter (53), so that the counter (53) receives a global clock signal ( instead of an impulse signal) ) to count the number of (S150).

[0084] Subsequent exposure time (T EXP ) is reached (S160). If the exposure time (T EXP) has not been reached, the global clock signal ( ) is accepted as is and continues to count (S150). However, the exposure time (T EXP ) is determined to have been reached, the count value currently counted in the counter (53) is obtained in each pixel (px) (S170).

[0085] And from the obtained count value, the pixel value (N PH ) is obtained (S180). At this time, the pixel value (N PH ) is the exposure time (T EXP ) and the number of overflows (N OF ) and the measurement time (T) obtained based on the count bit cell set in the count value. MEA ) is estimated from the overflow time (T OF ) can be calculated according to mathematical formula 1. However, each pixel value (N) according to the count value PH ) is selected according to the set count bit cell among a plurality of timing gain tables that are calculated and stored in advance, and then the pixel value (N) corresponding to the count value of the counter (53) is PH ) can also be obtained by exploring.

[0086] The pixel value of each of the multiple pixels (px) (N) PH ) are acquired, they are combined to acquire an image according to the light incident on the image sensor (S190).

[0087] Although FIG. 6 describes each process as being executed sequentially, this is merely an example, and those skilled in the art can modify and apply various modifications and variations, such as changing the order described in FIG. 6, executing one or more processes in parallel, or adding other processes, without departing from the essential characteristics of the embodiments of the present invention.

[0088] While the present invention has been described in detail above through representative examples, those skilled in the art will appreciate that various modifications and equivalent embodiments are possible. Therefore, the true scope of technical protection of the present invention should be determined by the technical spirit of the appended claims.

Claims

1. Contains a pixel array containing a plurality of pixels, Each of the above multiple pixels SPAD, which detects photons and generates impulse signals; A counter that counts the number of pulse signals applied; A multiplexer that selects one of a plurality of count bit cells of the counter according to a mode selection signal and outputs an overflow signal according to the bit value of the selected count bit cell; and An image sensor comprising a front module that converts the impulse signal into the pulse signal and, when the overflow signal is applied, converts a global clock signal into the pulse signal and transmits the converted signal to the counter.

2. In the first paragraph, the shear module An image sensor that drives the SPAD during a light detection operation and stops driving the SPAD when the overflow signal is applied.

3. In the first paragraph, the shear module An image sensor that converts the impulse signal or the global clock signal applied during a light detection operation into the pulse signal and transmits it to the counter until the exposure time is set.

4. In the first paragraph, the shear module An image sensor that receives the global clock signal by responding to the overflow signal once until the set exposure time.

5. In the first paragraph, the shear module An image sensor that resets the counter after a set exposure time.

6. In the first paragraph, the multiplexer An image sensor implemented in one of the above shear modules or the above counter.

7. In the first paragraph, the image sensor Including more control modules, The above control module is an image sensor that generates the mode selection signal and, after a set exposure time, receives a count value from the counter and obtains a pixel value.

8. In the 7th paragraph, the control module An image sensor that obtains the overflow count and overflow time from the count value according to the count bit cell of the counter selected according to the above mode selection signal, and calculates and obtains the pixel value by extrapolation based on the obtained overflow count and overflow time and the above exposure time.

9. In the 7th paragraph, the control module An image sensor that selects one of a plurality of timing gain tables in which pixel values ​​according to count values ​​are calculated in advance and stored, according to a selected count bit cell, and then searches for a pixel value corresponding to the count value in the selected timing gain table to obtain the pixel value.

10. In the 7th paragraph, the control module An image sensor that generates the mode selection signal by independently setting a count bit cell selected from each of the plurality of pixels.

11. A method of operating an image sensor including a pixel array composed of a plurality of pixels, each pixel having a SPAD and a counter, and a control module, A step of generating a mode selection signal for selecting one count bit cell among a plurality of count bit cells of the counter to output an overflow signal; A step of counting the number of impulse signals generated according to the photons detected by driving the SPAD; A step of generating an overflow signal in response to a bit value of a count bit cell selected according to the mode selection signal in the counter; and An operating method of an image sensor, comprising a step of counting a global clock signal when the above overflow signal is generated.

12. In the 11th paragraph, the step of counting the global clock signal An operating method of an image sensor that stops driving the SPAD when the above overflow signal is generated.

13. In the 11th paragraph, the step of counting the global clock signal An operating method of an image sensor that counts the global clock signal until a set exposure time.

14. In the 11th paragraph, the step of counting the global clock signal An operating method of an image sensor that receives the global clock signal and counts by responding to the overflow signal once until the set exposure time.

15. In the 11th paragraph, the step of counting the global clock signal An operating method of an image sensor that resets the count value of the counter after a set exposure time.

16. In the 11th paragraph, the operating method of the image sensor is An operating method of an image sensor further comprising a step of obtaining a pixel value by receiving a count value counted from the counter after a set exposure time.

17. In the 16th paragraph, the step of obtaining the pixel value is Obtain the overflow count and overflow time from the count value according to the count bit cell of the counter selected according to the above mode selection signal, An operating method of an image sensor that obtains the pixel value by calculating it using an extrapolation method based on the acquired number of overflows, the overflow time, and the exposure time.

18. In the 16th paragraph, the step of obtaining the pixel value is One of the multiple timing gain tables in which pixel values ​​according to each count value are pre-calculated and stored is selected according to the selected count bit cell, An operating method of an image sensor that searches for a pixel value corresponding to the count value in a selected timing gain table and obtains the pixel value.

19. In the 11th paragraph, the step of generating the mode selection signal An operating method of an image sensor that generates the mode selection signal by independently setting a count bit cell selected from each of the plurality of pixels.

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