Image sensor based on a single-photon avalanche diode and its driving method

Abstract

According to one embodiment of the present disclosure, a single-photon avalanche diode-based image sensor includes a single-photon avalanche diode (SPAD) that generates a plurality of pulses corresponding to each of a plurality of photons received during a predetermined exposure time, a front-end circuit that receives a set of pulses received during a portion of the exposure time among the plurality of pulses, and a counter that counts the number of pulses in the pulse set, and the end of the portion of the time can be based on an overflow point of the counter that counted the number of pulses in the pulse set.

Description

Technical Field

[0001] The present disclosure relates to a single photon avalanche diode-based image sensor and a driving method thereof.

[0002] The present invention was derived from research conducted as part of the General Department Whole Cycle Medical Device Research and Development Project of the government - other government agencies - General Department - General Department Whole Cycle Medical Device Research and Development Project - General Department Whole Cycle Medical Device Research and Development Project (issue unique number: 1711138024, detailed issue number: RS-2020-KD000048, research topic name: Development of a 20x20 cm large-area Hybrid X-ray video detector based on Global Shutter (2 / 2 stage) (1 / 2), supervisor: Rayence Co., Ltd., research period: March 1, 2022 to December 31, 2022). On the other hand, there is no property interest of the Korean government in all aspects of the present invention.

Background Art

[0003] A single photon avalanche diode (SPAD) is a sensing technology that senses a weak optical signal at the photon level. In particular, since the single photon avalanche diode utilizes avalanche multiplication that amplifies one incident photon, it has very high sensitivity and is very easy to use for photographing in dark places.

[0004] On the other hand, with such a single photon avalanche diode, an operation of counting trigger pulses generated by photons is required for photons. However, when using a counter with a large number of bits to count a large number of photons, there is a problem that the circuit scale becomes large and the power consumption increases.

Summary of the Invention

Problems to be Solved by the Invention

[0005] In order to solve the above-mentioned problems, this disclosure provides a single-photon avalanche diode-based image sensor that reduces power consumption by using the counter overflow time to estimate the total pulse (i.e., the total number of photons). [Means for solving the problem]

[0006] According to one embodiment of the present disclosure, a single-photon avalanche diode-based image sensor includes a single-photon avalanche diode (SPAD) that generates a plurality of pulses corresponding to each of a plurality of photons received during a predetermined exposure time, a front-end circuit that receives a set of pulses received during a portion of the exposure time, and a counter that counts the number of pulses in the pulse set, the endpoint of the portion of time may be based on the overflow point of the counter that counts the number of pulses in the pulse set.

[0007] According to one embodiment, the counter can count the number of clock pulses acquired through the front-end circuit during the exposure time after the overflow point.

[0008] According to one embodiment, each of the multiple clock pulses with respect to exposure time can be configured to include at least one shape among a log function, a linear function, or a square-root function.

[0009] According to one embodiment, the single-photon avalanche diode-based image sensor may further include a global clock that provides multiple clock pulses to the front-end circuitry from the time of overflow onward.

[0010] According to one embodiment, the total number of clock pulses generated by the global clock during exposure time can be configured to be the same as the number of pulses in the pulse set received during a portion of the time.

[0011] According to one embodiment, the single-photon avalanche diode-based image sensor may further include a processor that calculates the total number of photons received by the single-photon avalanche diode during the exposure time, using a first clock pulse generated by the global clock before the overflow time and a second clock pulse generated by the global clock after the overflow time.

[0012] According to one embodiment, the processor can calculate the total using a lookup table associated with the global clock.

[0013] According to one embodiment, the counter of a single-photon avalanche diode-based image sensor includes an N-bit counter, where one bit value among the N bits is associated with the overflow time, and the remaining bits among the N bits, excluding one bit, can be associated with values ​​obtained by counting multiple pulses.

[0014] According to other embodiments of the present disclosure, a single-photon avalanche diode-based image sensor driving method can include the steps of: receiving a plurality of photons for at least a fraction of a time within a predetermined exposure time by the single-photon avalanche diode; generating a plurality of pulses corresponding to each of the plurality of photons by the single-photon avalanche diode; receiving the plurality of pulses by a front-end circuit; and counting the plurality of pulses by a counter, wherein the endpoint of at least a fraction of a time is based on the overflow time of the counter that has counted the plurality of pulses.

[0015] According to other embodiments of the present disclosure, a computer-readable non-temporary recording medium can be provided on which a program for performing a single-photon avalanche diode-based image sensor driving method is recorded. [Effects of the Invention]

[0016] According to some embodiments of this disclosure, the power consumed by the counter can be significantly reduced by a method that counts only a portion of the total number of photons received by a single-photon avalanche and estimates the total number of photons by utilizing the counter's overflow time. [Brief explanation of the drawing]

[0017] [Figure 1] This block diagram shows the configuration of a single-photon avalanche diode substrate image sensor according to one embodiment of the present disclosure. [Figure 2] This graph illustrates a method for calculating the total number of photons received by a single-photon avalanche diode substrate image sensor according to one embodiment of the present disclosure. [Figure 3] This is a graph showing the clock pulses of a global clock provided to a front-end circuit according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0018] The specific details for implementing this disclosure will be described below with reference to the attached drawings. However, if the following explanation would unnecessarily obscure the essence of this disclosure, specific descriptions of widely known functions and configurations will be omitted.

[0019] In the attached drawings, identical or corresponding components are assigned the same reference numerals. Furthermore, in the following description of embodiments, identical or corresponding components may be omitted from the description. However, the omission of technical details regarding a component does not mean that such a component is not included in the given embodiment.

[0020] The advantages and features of the disclosed embodiments, and the methods for achieving them, will become clear by referring to the embodiments described later together with the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed below, and can be embodied in various different forms. The mere present embodiments are provided so that the present disclosure is complete, and the present disclosure is merely provided to fully inform those skilled in the art of the scope of the invention.

[0021] Briefly explain the terms used in this specification and specifically describe the disclosed embodiments. The terms used in this specification are selected as general terms that are currently widely used as possible while considering their functions in the present invention. However, this can change depending on the intentions or precedents of those skilled in the relevant fields, the emergence of new technologies, etc. Also, in certain cases, there are terms arbitrarily selected by the applicant. In this case, the meaning thereof will be described in detail in the explanatory part of the corresponding invention. Therefore, the terms used in the present disclosure should not be mere names of terms, but should be defined based on the meaning of the terms and the overall content of the present disclosure.

[0022] In this specification, the singular expressions include plural expressions unless it is specifically specified in the context that they are singular. Also, plural expressions include singular expressions unless it is specifically specified in the context that they are plural. Throughout the specification, when a given part "includes" a given component, this means that other components can be further included, rather than excluding other components, unless there is a special contrary description.

[0023] FIG. 1 is a block diagram showing the configuration of an image sensor 100 based on a single photon avalanche diode according to an embodiment of the present disclosure. Briefly, the image sensor 100 can receive a plurality of photons from the outside and generate an image by counting the number of the received plurality of photons. At this time, the image sensor 100 can consume a considerable amount of power to count photons. For this reason, in the present disclosure, an image sensor 100 is provided that reduces power consumption by counting only a predetermined number of photons and estimating the total number of received photons using information at the time when the corresponding counting ends. As shown in the figure, the image sensor 100 can include at least one of a single photon avalanche diode 110, a front-end circuit 120, and a counter 130.

[0024] The single photon avalanche diode 110 can receive a plurality of photons from the outside and generate a plurality of pulses corresponding to each of the received plurality of photons. For example, when N (where N is a natural number) photons are received by the single photon avalanche diode 110, the single photon avalanche diode 110 can generate N pulses. Thereafter, the generated plurality of pulses can be transmitted to the front-end circuit.

[0025] The single photon avalanche diode 110 can receive a plurality of photons from the outside during a pre-determined exposure time and generate a plurality of pulses corresponding to each of the received plurality of photons. For example, when N (where N is a natural number) photons are received by the single photon avalanche diode 110 from 0 [ms] to 16 [ms], the single photon avalanche diode 110 can generate N pulses. Thereafter, at least a part of the generated plurality of pulses can be transmitted to the front-end circuit.

[0026] The front-end circuit 120 can receive a plurality of pulses generated by the single-photon avalanche diode 110. In this case, the plurality of pulses can refer to the plurality of pulses received by the single-photon avalanche diode 110 during the exposure time. For example, when the front-end circuit 120 receives N (where N is a natural number) photons from 0 [ms] to 16 [ms] at the single-photon avalanche diode 110, it can receive N pulses from the single-photon avalanche diode 110. Additionally or alternatively, the front-end circuit 120 can receive at least some of the plurality of pulses generated by the single-photon avalanche diode 110. For example, when the front-end circuit 120 receives N (where N is a natural number) from 0 [ms] to 16 [ms] at the single-photon avalanche diode 110, it can receive NOF (where NOF < N) pulses received from 0 [ms] to TOF [ms] (where TOF < 16). As another example, when the front-end circuit 120 receives N (where N is a natural number) from 0 [ms] to 16 [ms] at the single-photon avalanche diode 110, it can receive NOF (where NOF < N) pulses received from TOF1 [ms] to TOF2 [ms] (where 0 < TOF1 < TOF2 <= 16).

[0027] The front-end circuit 120 can receive multiple clock pulses generated by an external device (e.g., a global clock). In this case, multiple clock pulses can refer to multiple clock pulses generated during the exposure time. For example, the front-end circuit 120 can receive M clock pulses from 0[ms] to 16[ms]. Additionally or alternatively, the front-end circuit 120 can receive multiple clock pulses generated during a portion of the total exposure time. For example, the front-end circuit 120 can receive clock pulses generated between TOF[ms] and 16[ms] during an exposure time from 0[ms] to 16[ms]. Alternatively, the front-end circuit 120 can receive clock pulses generated between 0[ms] and TOF[ms] during an exposure time from 0[ms] to 16[ms].

[0028] The front-end circuit 120 can start receiving multiple clock pulses generated by an external device in response to a signal received from the counter 130. In this case, the signal received from the counter 130 can refer to a signal generated in response to the counter 130 overflowing. More specifically, the signal received from the counter 130 can refer to a signal transmitted to the front-end circuit 120 in response to the counter 130 overflowing while counting multiple pulses received from the single-photon avalanche diode 110 through the front-end circuit 120. For example, if the exposure time is from 0 [ms] to 16 [ms], the N-bit counter 130 can use N-1 bits from 0 [ms] to receive from the single-photon avalanche diode 110 through the front-end circuit 120. 2 (N-1) piecesAfter counting the pulses, an overflow can occur. In this case, a value indicating the overflow is input to the remaining bit among the N bits of counter 130 that is not used for counting, and in response, counter 130 can transmit a signal to front-end circuit 120 at TOF [ms]. Subsequently, in response to the signal received from counter 130, front-end circuit 120 can stop receiving pulses from single-photon avalanche diode 110 and start receiving clock pulses from an external device. That is, front-end circuit 120 can receive multiple pulses from single-photon avalanche diode 110 from 0 [ms] until before TOF [ms], and multiple clock pulses from the external device from after TOF [ms] until 16 [ms].

[0029] The counter 130 can count the number of pulses input to the front-end circuit 120. For example, the counter 130 can count the number of pulses of multiple pulses input from the single-photon avalanche diode 110 to the front-end circuit 120 from 0 [ms] to before TOF [ms]. As an additional or alternative example, the counter 130 can count the number of multiple clock pulses input to the front-end circuit 120 from after TOF [ms] to 16 [ms].

[0030] On the other hand, although not shown in Figure 1, the image sensor 100 may further include a global clock (not shown) that generates the aforementioned clock pulses. In this case, the total number of clock pulses generated by the global clock during the exposure time may be the same as the number of pulses counted up to just before the N-bit counter 130 (in this case, only N-1 bits of the counter 130 are used for counting) overflows (i.e., before the TOF [ms] in the example above). That is, when an N-bit counter 130 is used, the total number of clock pulses generated by the global clock during the exposure time is 2 (N-1) pieces This can be pre-configured. A detailed explanation of this will be provided later in Figure 3.

[0031] Furthermore, while Figure 1 illustrates the image sensor 100 as containing one single-photon avalanche diode 110 for simplicity, it is not limited to this. That is, the image sensor 100 can contain multiple single-photon avalanche diodes. For example, the front-end circuit 120 can be connected to multiple single-photon avalanche diodes, each of which is located in a plurality of pixels.

[0032] Figure 2 is a graph 200 illustrating a method for calculating the total number of photons received by a single-photon avalanche diode-based image sensor (e.g., image sensor 100) according to one embodiment of the present disclosure. Here, it is assumed that a counter (e.g., counter 130) provided for counting pulses generated by the single-photon avalanche diode (e.g., single-photon avalanche diode 110) and / or a global clock is composed of N bits, and only N-1 bits are used for counting. The TOF in Figure 2 indicates the point in time when the counter overflows as a result of counting multiple pulses received from the single-photon avalanche diode.

[0033] As described above in Figure 1, the counter is generated by a single-photon avalanche diode during the time from 0 to TOF in order to conserve power. 2 (N-1) piecesOnly pulses will be counted. In this case, the time TEXP during which the image sensor is exposed to the light source has a predetermined value, so the total number of photons (NPH) received by the image sensor during the exposure time can be calculated according to Equation 1 below. In this case, the power saved by counting photons will be approximately NPH / NOF. NOF means the number of photons received by the image sensor from the time the image sensor is exposed to the light source until the counter overflows. On the other hand, in order to calculate the total number of photons (NPH) using Equation 1, it is first necessary to know the time of failure (TOF), which indicates the time when the counter overflows. The method for estimating TOF will be described later in Figure 3.

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[0034] Figure 3 is a graph 300 showing the clock pulses of a global clock provided to the front-end circuit according to one embodiment of the present disclosure. Similarly, a counter (e.g., counter 130) provided to count the pulses generated by a single-photon avalanche diode (e.g., single-photon avalanche diode 110) and / or the global clock is assumed to consist of N bits, with only N-1 bits used for counting. TOF and TEXP also indicate the time when each counter overflows and the time when the single-photon avalanche diode is exposed to a light source, as shown in TOF and TEXP in Figure 2.

[0035] As described above in Figure 1, the total number of clock pulses M generated during the exposure time is equal to the number of pulses generated by the single-photon avalanche diode between 0 and TOF (i.e., 2 (N-1) piecesIt is set to be identical to ). Furthermore, each timing of the overall clock pulse is set to include at least one function from a log function, a linear function, or a square-root function with respect to the exposure time. For example, clock pulses from 0 to TOF can be provided in linear function form, and clock pulses from TOF to TEXP can be provided in log function form. That is, each timing of the overall clock pulse will have a predetermined value based on the shape of the selected function. Therefore, the timing (Tn) of the latest clock pulse before TOF can be calculated using the order (here, n+1) and timing (Tn+1) of the earliest clock pulse that occurred after TOF. At this time, the counter overflow occurs at a timing between Tn and Tn+1, so TOF can be estimated to be any value between NOF*(TEXP / Tn) and NOF*(TEXP / Tn+1) as shown in equation 2 below.

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[0036] The preceding explanations in this disclosure are provided to enable a person of ordinary skill to perform or utilize this disclosure. Various modifications of the invention are readily apparent to a person of ordinary skill, and the general principles defined herein may be applied to various modifications without departing from the spirit or scope of the invention. Accordingly, this disclosure is not intended to be limited to the examples described herein, but rather to provide the broadest scope consistent with the principles and novel features disclosed herein.

[0037] While this disclosure has been described in relation to some embodiments, it should be understood that various modifications and alterations can be made without departing from the scope of this disclosure as understandable to a person ordinary in the art to which the invention pertains. Furthermore, such modifications and alterations should be considered to fall within the scope of the claims appended herein.

Claims

1. A single-photon avalanche diode (SPAD) generates multiple pulses corresponding to each of the multiple photons received during a predetermined exposure time, A front-end circuit that receives a set of pulses among the plurality of pulses that are received during a portion of the exposure time, A counter that counts the number of pulses in the pulse set, The front-end circuit is provided with a global clock that provides clock pulses during the exposure time, A processor that calculates the total number of photons received by the single-photon avalanche diode during the aforementioned exposure time, Includes, The end point of the aforementioned time period is determined based on the overflow point of the counter that counts the number of pulses in the pulse set, The counter counts the number of clock pulses acquired through the front-end circuit during the exposure time after the overflow point. Each of the multiple clock pulses with respect to the exposure time has a value predetermined based on the shape of the function, The processor calculates the timing of the latest clock pulse that occurred before the overflow point using the order and timing of the earliest clock pulse that occurred after the overflow point, estimates the overflow point of the counter at the time between the timing of the latest clock pulse that occurred before the overflow point and the timing of the earliest clock pulse that occurred after the overflow point, and calculates the total number using the estimated overflow point of the counter and a lookup table associated with the global clock, in a single-photon avalanche diode substrate image sensor.

2. The single-photon avalanche diode substrate image sensor according to claim 1, wherein each time point of the plurality of clock pulses with respect to the exposure time is configured to include at least one shape from a log function, a linear function, or a square-root function.

3. The single-photon avalanche diode substrate image sensor according to claim 1, wherein the total number of clock pulses generated by the global clock during the exposure time is the same as the number of pulses in the pulse set received during the partial time.

4. The image sensor based on a single-photon avalanche diode according to claim 1, wherein the processor calculates the total number of photons received by the single-photon avalanche diode during the exposure time using a first clock pulse generated by the global clock before the overflow time and a second clock pulse generated by the global clock after the overflow time.

5. The aforementioned counter includes an N-bit counter, The single-photon avalanche diode substrate image sensor according to claim 1, wherein the value of one bit among the N bits is associated with the overflow time, and the remaining bits among the N bits, excluding the one bit, are associated with a value obtained by counting the plurality of pulses.

6. A step of receiving multiple photons for at least a portion of the predetermined exposure time using a single-photon avalanche diode, The steps include generating a plurality of pulses corresponding to each of the plurality of photons using the single-photon avalanche diode, The steps include receiving the plurality of pulses by the front-end circuit, The steps include counting the plurality of pulses using a counter, Includes, The endpoint of at least a portion of the time is configured to be based on the overflow point of the counter that counts the plurality of pulses, The steps include providing the front-end circuit with a clock pulse during the exposure time using a global clock, The steps include counting the number of clock pulses obtained through the front-end circuit during the exposure time after the overflow point using the counter, A step of calculating the total number of photons received by the single-photon avalanche diode during the exposure time using a processor, It further includes, Each of the multiple clock pulses with respect to the exposure time has a value predetermined based on the shape of the function, A method for driving an image sensor based on a single-photon avalanche diode, comprising the steps of calculating the total number, which include: using the order and timing of the earliest clock pulse that occurred after the overflow time to calculate the timing of the latest clock pulse that occurred before the overflow time; estimating the overflow time of the counter at the time between the timing of the latest clock pulse that occurred before the overflow time and the timing of the earliest clock pulse that occurred after the overflow time; and using the estimated overflow time of the counter and a lookup table associated with the global clock to calculate the total number of photons received by the single-photon avalanche diode during the exposure time.

7. A computer-readable non-temporary recording medium on which a program for performing the single-photon avalanche diode substrate image sensor driving method described in claim 6 is recorded.

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