Single-photon avalanche diode-based image sensor and driving method thereof

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] This invention has been derived from research conducted as part of the Korean government-other government agencies-Korean government ... [Background technology]

[0003] Single-Photon Avalanche Diode (SPAD) is a sensing technology that detects faint light signals at the photon level. In particular, SPAD uses avalanche multiplication, which amplifies a single incident photon, making it highly sensitive and very easy to use for imaging in dark places.

[0004] Meanwhile, in such single-photon avalanche diodes, photons require the operation of counting trigger pulses generated by photons. However, if a counter with a large number of bits is used to count a large number of photons, the circuit size becomes large, which increases power consumption. Summary of the Invention [Problem to be solved by the invention]

[0005] In order to solve the above-mentioned problem, the present disclosure provides a single-photon avalanche diode-based image sensor that reduces power consumption by estimating the total number of pulses (i.e., total photons) using the overflow point of a counter. [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 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.

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

[0008] According to one embodiment, the time points of each of the plurality of clock pulses relative to the 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 a plurality of clock pulses to the front-end circuitry after the overflow point.

[0010] According to one embodiment, the number of total clock pulses generated by the global clock during an 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 an exposure time using a first clock pulse generated by the global clock before the overflow point and a second clock pulse generated by the global clock after the overflow point.

[0012] According to one embodiment, the processor may calculate the total number using a look-up table associated with the global clock.

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

[0014] According to another embodiment of the present disclosure, a method for driving a single-photon avalanche diode-based image sensor may include receiving a plurality of photons during at least a portion of a predetermined exposure time by a 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 an end point of the at least a portion of the time may be configured based on an overflow point of the counter that counted the plurality of pulses.

[0015] According to another embodiment of the present disclosure, a computer-readable non-transitory recording medium having a program recorded thereon for executing a method for driving a single-photon avalanche diode-based image sensor may be provided. [Effects of the Invention]

[0016] According to some embodiments of the present disclosure, the power consumed by the counter can be significantly reduced by counting only a portion of the total photons received in a single-photon avalanche and estimating the total number of photons using the counter overflow time. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a block diagram illustrating a configuration of a single-photon avalanche diode-based image sensor according to an embodiment of the present disclosure. [Figure 2] 1 is a graph illustrating a method for calculating the total number of photons received by a single-photon avalanche diode-based image sensor according to an embodiment of the present disclosure. [Figure 3] 4 is a graph illustrating clock pulses of a global clock provided to provide clock pulses to a front-end circuit according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, specific details for implementing the present disclosure will be described in detail with reference to the accompanying drawings, provided that in the following description, detailed descriptions of well-known functions and configurations will be omitted if they may unnecessarily obscure the gist of the present disclosure.

[0019] In the accompanying drawings, identical or corresponding components are denoted by the same reference numerals. In addition, in the following description of the embodiments, redundant description of identical or corresponding components may be omitted. However, the omission of technology related to a component does not mean that such a component is not included in a given embodiment.

[0020] The advantages and features of the disclosed embodiments, and methods for achieving them, will become apparent from the following description of the embodiments in conjunction with the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed below, and may be embodied in various different forms. The present embodiments are merely provided so that the disclosure will be complete and will fully convey the scope of the invention to those skilled in the art.

[0021] The terms used in this specification will be briefly explained, and then the disclosed embodiments will be specifically described. The terms used in this specification have been selected based on the functions of the present invention and are currently widely used. However, these terms may change depending on the intentions of engineers in the relevant field, precedents, the emergence of new technologies, etc. In addition, in certain cases, the applicant may arbitrarily select terms, and in such cases, their meanings will be described in detail in the relevant description of the invention. Therefore, the terms used in this disclosure should be defined based on the meanings of the terms and the overall content of this disclosure, rather than simply by their names.

[0022] In this specification, the singular includes the plural unless the context clearly dictates otherwise. Furthermore, the plural includes the singular unless the context clearly dictates otherwise. Throughout the specification, when a certain part 'comprises' certain elements, this does not mean that other elements are excluded, but that other elements may also be included, unless specifically stated to the contrary.

[0023] FIG. 1 is a block diagram illustrating a configuration of a single-photon avalanche diode-based image sensor 100 according to an embodiment of the present disclosure. Briefly, the image sensor 100 receives a plurality of photons from an external source and generates an image by counting the number of received photons. In this case, the image sensor 100 may consume a considerable amount of power to count photons. To address this, the present disclosure provides an image sensor 100 that reduces power consumption by counting photons up to a predetermined number and estimating the total number of received photons using information regarding when the counting ends. As illustrated, the image sensor 100 includes 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 multiple photons from the outside and generate multiple pulses corresponding to each of the received photons. For example, if N photons (where N is a natural number) are received by the single-photon avalanche diode 110, the single-photon avalanche diode 110 can generate N pulses. The generated pulses can then be transmitted to a front-end circuit.

[0025] The single-photon avalanche diode 110 can receive multiple photons from the outside during a predetermined exposure time and generate multiple pulses corresponding to each of the received photons. For example, if the single-photon avalanche diode 110 receives N photons from 0 ms to 16 ms (where N is a natural number), the single-photon avalanche diode 110 can generate N pulses. At least some of the generated pulses can then be transmitted to a 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 the single-photon avalanche diode 110 from 0 [ms] to 16 [ms], the front-end circuit 120 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 the single-photon avalanche diode 110 from 0 [ms] to 16 [ms], the front-end circuit 120 can receive NOF (where NOF < N) pulses received from 0 [ms] to TOF [ms] (where TOF < 16). For another example, when the front-end circuit 120 receives N (where N is a natural number) from the single-photon avalanche diode 110 from 0 [ms] to 16 [ms], the front-end circuit 120 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 may receive multiple clock pulses generated by an external device (e.g., a global clock). In this case, the multiple clock pulses may refer to multiple clock pulses generated during the exposure time. For example, the front-end circuit 120 may receive M clock pulses from 0 ms to 16 ms. Additionally or alternatively, the front-end circuit 120 may receive multiple clock pulses generated during a portion of the entire exposure time. For example, the front-end circuit 120 may receive clock pulses generated after TOF [ms] and up to 16 ms within the exposure time from 0 ms to 16 ms. For another example, the front-end circuit 120 may receive clock pulses generated between 0 ms and TOF [ms] within the exposure time from 0 ms to 16 ms.

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

[0029] Counter 130 may count the number of pulses input to front-end circuit 120. For example, counter 130 may count the number of pulses input from single-photon avalanche diode 110 to front-end circuit 120 from 0 [ms] to before TOF [ms]. Additionally or alternatively, counter 130 may count the number of clock pulses input to front-end circuit 120 from after TOF [ms] to 16 [ms].

[0030] Meanwhile, although not shown in FIG. 1, the image sensor 100 may further include a global clock (not shown) that generates the above-mentioned 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 until just before the N-bit counter 130 (in which only N-1 bits of the counter 130 are used for counting) overflows (i.e., before TOF [ms] in the above example). In other words, when the N-bit counter 130 is used, the total number of clock pulses generated by the global clock during the exposure time may be preset to 2(N-1). This will be described in detail later with reference to FIG. 3.

[0031] 1 illustrates the image sensor 100 as including one single-photon avalanche diode 110 for ease of explanation, but is not limited to this. That is, the image sensor 100 may include multiple single-photon avalanche diodes. For example, the front-end circuit 120 may be connected to multiple single-photon avalanche diodes arranged in multiple pixels, respectively.

[0032] 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 an embodiment of the present disclosure. Here, it is assumed that a counter (e.g., counter 130) provided for counting pulses generated by a single-photon avalanche diode (e.g., single-photon avalanche diode 110) and / or a global clock is configured with N bits, and only N-1 bits are used for counting. Also, TOF in FIG. 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 shown in FIG. 1, the counter counts only 2(N-1) pulses generated by the single-photon avalanche diode between 0 and TOF to conserve power consumption. In this case, the time TEXP during which the image sensor is exposed to the light source is 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 required to count photons is saved by NPH / NOF. NOF refers to the number of photons received by the image sensor from the time the image sensor begins to be exposed to the light source until the counter overflows. To calculate the total number of photons (NPH) using Equation 1, the TOF, which indicates the time the counter overflows, must first be known. A method for estimating TOF is described below with reference to FIG. 3.

number

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

[0035] As described above with reference to FIG. 1, the number M of total clock pulses generated during the exposure time is set to be equal to the number of pulses (i.e., 2(N-1)) generated by the single-photon avalanche diode between 0 and TOF. The timing of each of the total clock pulses is set to include at least one of a logarithmic function, a linear function, or a square-root function with respect to the exposure time. For example, clock pulses between 0 and TOF may be provided in the form of a linear function, and clock pulses between TOF and TEXP may be provided in the form of a logarithmic function. That is, the timing of each of the total clock pulses has a predetermined value based on the shape of the selected function. Therefore, the time (Tn) of the latest clock pulse before TOF can be calculated using the order (here, n+1) and time (Tn+1) of the earliest clock pulse after TOF. In this case, since the counter overflow occurs between Tn and Tn+1, TOF can be estimated as any value between NOF*(TEXP / Tn) and NOF*(TEXP / Tn+1) as shown in the following equation 2.

number

[0036] The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications of the present invention will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to various variations without departing from the spirit or scope of the present invention. Thus, the present disclosure is not intended to be limited to the examples described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0037] Although the present disclosure has been described herein with reference to certain embodiments, it should be understood that various modifications and changes that would be apparent to one of ordinary skill in the art to which the present invention pertains can be made without departing from the scope of the present disclosure, and such modifications and changes are to be considered to fall within the scope of the claims appended hereto.

Claims

1. 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 for receiving a set of pulses from the plurality of pulses received during a portion of the exposure time; a counter that counts the number of pulses in the pulse set; Including, The end point of the partial time period is based on an overflow point of the counter that counts the number of pulses in the pulse set.

2. 2. The single-photon avalanche diode-based image sensor of claim 1, wherein the counter counts the number of clock pulses obtained through the front-end circuit during the exposure time after the overflow point.

3. 3. The single-photon avalanche diode-based image sensor of claim 2, wherein the time points of the plurality of clock pulses relative to the exposure time are configured to have at least one shape selected from the group consisting of a log function, a linear function, and a square-root function.

4. A global clock that provides a plurality of clock pulses to the front-end circuitry after the overflow time. The single-photon avalanche diode-based image sensor of claim 1 , further comprising:

5. 5. The single-photon avalanche diode-based image sensor of claim 4, wherein the number of total 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 portion of the time.

6. 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; The single-photon avalanche diode-based image sensor of claim 4 , further comprising:

7. The single-photon avalanche diode-based image sensor of claim 6 , wherein the processor calculates the total number using a look-up table associated with the global clock.

8. the counter includes an N-bit counter; 2. The single-photon avalanche diode-based image sensor of claim 1, wherein a value of one bit among the N bits is associated with the overflow time point, and the remaining bits other than the one bit among the N bits are associated with a value obtained by counting the pulses.

9. receiving a plurality of photons during at least a portion of a predetermined exposure time with a single-photon avalanche diode; generating a plurality of pulses corresponding to each of the plurality of photons with the single-photon avalanche diode; receiving the plurality of pulses with a front-end circuit; counting the plurality of pulses with a counter; Including, The method for driving a single-photon avalanche diode-based image sensor is configured such that the end point of the at least part of the time period is based on an overflow point of the counter that counts the plurality of pulses.

10. A non-transitory computer-readable recording medium having a program recorded thereon for executing the method of driving a single-photon avalanche diode-based image sensor according to claim 9.

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