System and method for detecting, locating, and signaling single-photon events and at least two-photon time-coincident events.

Abstract

The present invention relates to a system and method for the detection, localization and signaling of single photon events and at least two-photon time coincidence events. The system (100) comprises at least one array (M;MM) of pixels (10), each of which has a photodetector (12) and a digital signal (Sd1, ..., Sd x The system (100) further comprises at least one event detection electronics (20) including a plurality of digital-to-analog converters (21), one for each pixel (10) of the array (M;MM), an analog summer node (22), and an overall analog-to-digital converter (24). The plurality of digital-to-analog converters (21) convert the digital signals (Sd1, ..., Sd1) coming from each pixel (10) into a digital signal (Sd1, ..., Sd1) coming from each pixel (10). x ) to the corresponding analog signals (Sa1, ..., Sa x ) to the corresponding analog signals (Sa1, ..., Sa x ) are quantized in amplitude and duration. The analog adder node (22) adds the analog signals (Sa1, ..., Sa x) to obtain a total analog signal (Sa). The integrated analog-to-digital converter (24) comprises at least one first comparator (25) and a second comparator (26) operatively connected to the analog summer node (22). The first comparator (25) is configured to compare the output signal (Sout) of the analog summer node (22) with a first threshold (TH1) corresponding to triggering a number of pixels within the coincidence time window that is equal to or greater than a first predetermined value. The second comparator (26) is configured to compare the output signal (Sout) of the analog summer node (22) with a second threshold (TH2) corresponding to triggering a number of pixels within the coincidence time window that is equal to or greater than a second predetermined value. The first comparator (25) and the second comparator (26) generate a digital signal (Sd) when the output signal (Sout) of the analog summer node exceeds a first threshold (TH1) or a second threshold (TH2), respectively, to enable event detection when the number of incident photons on the array (M;MM) is equal to or exceeds a first value or a second value of the triggered pixel (10) within the time coincidence window. 1F , ..., Sd yF ) to output.

Description

[Technical Field]

[0001] The present invention relates to the technical field of photon detection systems. In particular, the present invention relates to systems and methods for detecting, locating, and signaling single-photon events and at least two-photon time coincidence events.

[0002] The present invention is particularly applicable to, but not limited to, medical imaging, fluorescence imaging, spectroscopy, quantum microscopy, direct and indirect measurement of time-of-flight (ToF), and light-based object distance detection (Light Detection and Ranging or Laser Imaging Detection and Ranging: LiDAR). For example, it can be used in applications such as autonomous vehicles, geodesy, and altitude measurement. [Background technology]

[0003] In recent years, the field of photon detection has made significant progress due to the increasing demand for devices that can provide state-of-the-art performance in photon detection across many scientific and technological fields.

[0004] When it is necessary to detect very weak optical signals, it is known to use single-photon detectors, such as SPAD (Single-Photon Avalanche Diode) photodetectors configured as a single or SPAD array, or SiPM (Silicon Photomultiplier Tube) photodetectors.

[0005] SPAD photodetectors are essentially composed of pn junctions and are retropolarized (breakdown) at voltages higher than the avalanche voltage. When a photon collides with the SPAD, an electron-lacuna pair is generated, triggering an avalanche process in which the charge multiplies very rapidly (hundreds of ps), and a macroscopic current signal (on the order of milliamperes) is output. This operating region is defined as the Geiger mode. The elapsed time between the quiescent state of the SPAD and the trigger of the avalanche multiplication, which coincides with the rising edge of the current signal, records the arrival time of the photon.

[0006] Therefore, the SPAD photodetector operates like a photon-triggered sensor, converting a single photon into a macroscopic current consisting of countless electrons and gaps.

[0007] Conventional SPAD photodetector arrays typically comprise multiple independent pixels, each pixel comprising a SPAD photodetector, readout or front-end electronics (analog or digital), and, where applicable, additional electronics configured to perform a timestamp of arrival time by counting the number of photons arriving at the SPAD or, for example, measuring the time of flight of each photon with respect to a reference synchronization.

[0008] The output of each pixel is processed entirely digitally, maintaining the advantages of SPAD photodetectors, which are unaffected by readout noise, and effectively providing information about the intensity (by photon counting) and / or waveform (by measuring the arrival time of photons) of the optical signal.

[0009] The array of SPAD photodetectors is typically read by scanning each pixel row by row. This allows for the storage of spatial information (x,y) of the photon collision, i.e., the position of the triggered pixel in the array. For example, since the counters of each pixel are read in a known order, it becomes possible to reconstruct a two-dimensional 2D intensity map, i.e., the position (x,y) and number of detected photons, or a three-dimensional 3D map, i.e., the position (x,y) and arrival time t of the detected photons, or the distance z from the pixel in the array to the object.

[0010] The output of a SPAD photodetector array is typically a digital bus, providing pixel content (such as the number of detected photons and their arrival times) at a predetermined frame rate.

[0011] Despite the advantages of SPAD arrays, such as their tolerance to readout noise and spatial resolution—that is, their ability to store information about the position of the array pixels where photons collide—they also have several drawbacks.

[0012] Firstly, because these arrays are entirely digital, it is impossible to detect the phenomenon of time synchronization or time correlation of photons striking the array. This problem is usually solved by incorporating timing electronics configured to timestamp the photons into each pixel of the array. The timestamps of the detected photons are then processed, and pixels with the same timestamp as the detected photons are identified.

[0013] As a result, each pixel in the SPAD array requires fairly complex timing electronics, which impairs the array's fill factor, i.e., the ratio of the SPAD's active photon-sensitive region to the entire pixel area. Data post-processing steps are also required.

[0014] Secondly, acquiring fixed-frequency frames is disadvantageous when applied in situations with low photon flux. This is because the system can become overloaded with redundant data, such as frames with no evidence of incident photons or frames with many pixels that do not contain useful data, negatively impacting power consumption, the amount of data transmitted, the amount of data processed, and therefore the bandwidth of the read channel, memory availability, and the necessary retrieval and storage work of the microprocessor. In these types of applications, it is convenient to use an event-driven readout approach if the expected event can be detected directly on the chip (rather than in a later process). An event could be, for example, the detection of one photon in one pixel, the simultaneous detection of two photons in two different pixels, or the detection of N photons in N different pixels.

[0015] For SPAD arrays configured to detect single-photon events, maintain spatial resolution, and be event-driven, see, for example, "A CMOS 64×48 Single Photon Avalanche Diode Array with Event-Driven Readout" by C. Niclass, M. Sergio, and E. Charbon, pp. 556-559 of the Proceedings of the 32nd European Solid-State Circuits Conference, 2006; "A 100-m Range 10-Frame / s 340×96-Pixel Time-of-Flight Depth Sensor in 0.18-μm CMOS" by C. Niclass, M. Soga, H. Matsubara, S. Kato, and M. Kagami, pp. 559-572 of the IEEE Journal of Solid-State Circuits, Vol. 48, No. 2, 2013; and A. Berkovich, T. Datta, and P. This is described in Abshire's presentation 1110-1113, "A scalable 20×20 fully asynchronous SPAD-based imaging sensor with AER readout," at the 2015 IEEE International Symposium on Circuits and Systems (ISCAS).

[0016] SiPM is an analog photodetector consisting of an array of microcells that operate like a single pixel. Each microcell contains a SPAD with a quenching resistor, which is connected between the output of the SPAD and a node common to the entire array. The quenching resistor prevents the avalanche multiplication generated by electron-hole pairs produced when a photon collides with the microcell. In this way, the microcell can rapidly detect subsequent photon incidences.

[0017] The output signal of a SiPM is typically provided by a single analog current. This analog current is equal to the sum of the output analog currents of each microcell and is generated by photon detection, and is therefore a function of the number of photons incident on all microcells of the SiPM.

[0018] SiPMs have the advantage of providing a large active region, given by the sum of the active regions of all SPADs, and the advantage of providing information about the number of photons that drove different microcells individually or simultaneously, i.e., photon number resolution. In fact, by measuring the amplitude of the output analog current, it is possible to know the number of photons that collided with the photodetector simultaneously (or nearly simultaneously).

[0019] Therefore, SiPM is an event-driven detector that supplies analog current only when one or more SPADs are triggered, and is particularly well-suited for detecting photon coincidence, i.e., when several photons collide with several microcells at approximately the same time.

[0020] However, despite its many advantages, SiPM has many drawbacks, primarily related to its analog nature.

[0021] In fact, SiPMs are susceptible to high readout noise. Furthermore, because it is impossible to know which SPAD a photon hit, the spatial information (x,y) associated with the detected photon is lost. For this reason, SiPMs operate as a single pixel. In addition, SiPMs are not easily scalable (i.e., scalable to the ever-increasing number of microcells) because the common node becomes overloaded with parasitic capacitance and leakage current, making it difficult to accurately determine the arrival time and the number of detected photons. Moreover, propagation delays occur as the size increases, limiting the ability to accurately detect the simultaneous counting of multiple photons incident on the photodetector at the same time.

[0022] For example, pages 1-3 of the 2018 IEEE Nuclear Science Symposium and Medical Imaging Conference Proceedings by A. Muntean et al., titled "Fully Integrated State-of-the-Art Analog SiPM with on-chip Time Conversion," describe a scalable analog SiPM configured to identify single-photon events.

[0023] Digital SiPMs are often used to eliminate or reduce readout noise. In a digital SiPM, each microcell is equipped with a digital front-end circuit instead of a quenching resistor, generating a digital signal each time avalanche multiplication is triggered by the SPAD. Meanwhile, control logic suppresses the avalanche and reactivates the SPAD after a predetermined time. The digital output of each microcell is sent to a single digital node, usually an OR logic port, which generates a digital signal synchronized with the first detected photon.

[0024] Similar to analog SiPMs, digital SiPMs behave like single pixels and do not provide spatial information about which SPAD in the array was triggered by the incident photon.

[0025] A digital SiPM configured to identify simultaneous counting events of photons across an entire array of microcells or within a macroscopic region of microcells is described, for example, on pages 1959–1965 of the 2009 IEEE Nuclear Science Symposium Conference Record by T. Frach, G. Prescher, C. Degenhardt, R. de Gruyter, A. Schmitz, and R. Ballizany, titled "The digital silicon photomultiplier - Principle of operation and intrinsic detector performance."

[0026] State-of-the-art SiPM arrays are also known, that is, arrays in which each pixel is composed of analog or digital SiPMs. Examples of such arrays are known from "A 64×64-Pixels Digital Silicon Photomultiplier Direct TOF Sensor With 100-MPhotons / s / pixel Background Rejection and Imaging / Altimeter Mode With 0.14% Precision Up To 6 km for Spacecraft Navigation and Landing" by M. Perenzoni, D. Perenzoni, and D. Stoppa, Vol. 52, No. 1, pp. 151-160, 2017, and "Multipurpose, Fully Integrated 128×128 Event-Driven MD-SiPM With 512 16-Bit TDCs with 45-ps LSB and 20-ns Gating in 40-nm CMOS Technology" by A. Carimatto et al., Vol. 1, No. 12, December 2018, pp. 241-244.

[0027] European Patent No. 3341755 (EP3341755B1) describes a photon counting device configured to record simultaneous interactions between adjacent pixels when such interactions occur within a very narrow simultaneous counting window. This device cannot detect interactions between distant pixels and therefore does not provide spatial information.

[0028] European Patent Application Publication No. 3502636 (EP3502636A1) describes a solution for counting and timestamping photon time-simultaneous counting events. This solution is very similar to a SiPM photodetector and does not provide spatial information regarding multiple photon time-simultaneous counting events.

[0029] As an attempt to overcome the shortcomings of the aforementioned analog-only or digital-only detectors, mixed analog-digital systems have been proposed.

[0030] U.S. Patent Application Publication No. 2019 / 0259792 (US2019 / 0259792A1) describes an analog-digital mixed system for detecting the time-simultaneous counting of two or more photons in a SPAD array. This mixed system has a single common adder node, which significantly limits the number of pixels in the array and impairs overall reliability and noise immunity. Furthermore, since all pixels in the array act as a single overall detector similar to a SiPM, spatial information of the incident photons is not preserved. [Prior art documents] [Patent Documents]

[0031] [Patent Document 1] European Patent No. 3341755 [Patent Document 2] European Patent Application Publication No. 3502636 [Patent Document 3] U.S. Patent Application Publication No. 2019 / 0259792 Specification [Overview of the Initiative]

[0032] The objective of this invention is to overcome the shortcomings of the prior art.

[0033] Specifically, the object of the present invention is to provide a system and method for detecting photons that are configured to directly detect both single-photon events and time-coincident counting events of at least two photons within a given time window, on-chip, while maintaining immunity to noise.

[0034] Another objective of the present invention is to provide a system and method for detecting photons that can optimize computational resources for processing detection signals while minimizing bottlenecks in data transmission, processing, and storage.

[0035] Another object of the present invention is to provide a system and method for detecting photons configured to maintain the spatial resolution of a pixel array in the detection of photons, that is, to provide spatial information regarding the location where a photon is detected.

[0036] Another objective of the present invention is to provide a modular system for detecting photons that allows the system to be expanded without compromising its performance.

[0037] These and other objects of the present invention are achieved by systems and methods for detecting photons incorporating features of the appended claims that form an integral part of this description.

[0038] According to a first aspect, the present invention relates to a system for detecting photon events comprising at least one pixel array, each pixel comprising a photodetector and a front-end electronic device that outputs a digital signal.

[0039] Furthermore, the detection system includes at least one event detection electronic device, and the event detection electronic device is - A plurality of digital-to-analog converters, one for each pixel in the array, each digital-to-analog converter is configured to convert the digital signal coming from each pixel into a corresponding analog signal, the corresponding analog signal being quantized by amplitude and duration, - An analog adder node comprising multiple digital-to-analog converters operably connected, wherein the analog adder node is configured to add the analog signals coming from the digital-to-analog converters to obtain a total analog signal, - An integrated analog-to-digital converter comprising at least one first comparator and a second comparator operably connected to an analog adder node, Includes, The first comparator is configured to compare the output signal of the analog adder node with a first threshold corresponding to a trigger for a number of pixels greater than or equal to a first predetermined value within the time synchronization window. The second comparator is configured to compare the output signal of the analog adder node with a second threshold corresponding to a trigger for a number of pixels greater than or equal to a second predetermined value within the time synchronization window. The first and second comparators are configured to output a digital signal when the output signal of the analog adder node exceeds a first threshold or a second threshold, respectively, so that event detection is possible when the number of incident photons into the array exceeds a first predetermined value or a second predetermined value within a time synchronization window.

[0040] The combination of these characteristics, particularly the presence of a mixed digital and analog processing chain for photon detection within the system, results in a photon detection system that maintains the noise immunity inherent in SPADs while providing on-chip localization and signaling for single-photon events and multi-photon time-coincident events. Furthermore, because readout is event-driven, the system transmits output data to external (off-chip) electronic equipment, for example, only when a single-photon event or a multi-photon time-coincident event is detected. As a result, event signaling is driven, and only useful data is signaled and transmitted to off-chip electronic equipment, thus optimizing system-level resources.

[0041] In one embodiment, the first threshold corresponds to a trigger with 1 or more pixels, and the second threshold corresponds to a trigger with 2 or more pixels.

[0042] In one embodiment, the system preferably includes a multiplexer, which is configured to generate a digital signal indicating the detection of an event when a user-defined threshold of time-coincidentally counted photons is reached.

[0043] In one embodiment, each pixel in the array is equipped with an event-driven read electronic device configured to transmit the address of the triggered pixel to a common address line when an event detection signal is generated.

[0044] In one embodiment, the event-driven reading electronic device for each pixel comprises a pixel state sampling block, an address writing block, and a block for monitoring the common state of the address line, and all blocks communicate with an open-drain serial port equipped with a global pull-up resistor.

[0045] In one embodiment, a large number of addresses, for example, more addresses than the number of pixels triggered within a time window, are sent to the common address line. This has the advantage of maintaining the spatial resolution of pixels in the array.

[0046] In one embodiment, the system comprises a mother array divided into arrays, where the event detection electronics of the arrays are connected to each other in seamless cascaded connections, and the last event detection electronics in the cascaded connections is connected to an output block. Additional stages of signal regeneration are preferably avoided, and the modular structure of the mother array also ensures the scalability of the pixels and the mother array.

[0047] In one embodiment, the cascaded connection of the array's event detection electronics follows a path having an H-tree fractal recursive branch.

[0048] In one embodiment, the analog adder node includes a transimpedance amplifier.

[0049] In one embodiment, each pixel's photodetector is a SPAD (Single-Phase Photodetector).

[0050] According to a second aspect, the present invention is also directed to a method for detecting photons, the method comprising the following steps: - A step of generating at least one digital signal in response to a photon collision with one or more pixels of at least one pixel array, - A step of converting the digital signal coming from each triggered pixel into a corresponding analog signal quantized by amplitude and duration, - The analog adder node adds the quantized analog signals and obtains an analog total signal; this is the summing step. - A step of converting the output signal of an analog adder node into at least two digital signals, each of which becomes a high logic value when the analog signal exceeds two respective thresholds, Includes, The analog-to-digital conversion step involves at least the following steps: - A step of comparing the output signal of the analog adder node with a first threshold corresponding to a number of pixels greater than or equal to a first predetermined value within the time synchronization window, - A step of comparing the output signal of the analog adder node with a second threshold corresponding to a second predetermined number of pixels or more within the time synchronization window that triggers, - A step of generating a digital signal when the output signal of an analog adder node exceeds a first threshold or a second threshold, respectively, so that event detection is possible when the number of incident photons to the array exceeds a first predetermined value or a second predetermined value within a time synchronization window, Includes.

[0051] In one embodiment, the first threshold corresponds to a trigger with 1 or more pixels, and the second threshold corresponds to a trigger with 2 or more pixels.

[0052] In one embodiment, the method includes an initial step of selectively activating pixels of an array to sense incident photons, and the method includes a step of checking for the exceedance of a threshold set by the user. If the threshold is not exceeded, follow these steps: - A step of generating at least one digital signal in response to a photon collision with one or more pixels of at least one pixel array, - A step of converting the digital signal coming from each pixel into a corresponding analog signal that is quantized by amplitude and duration, - The analog adder node adds analog signals together to obtain an analog total signal; - A step of converting the output signal of an analog adder node into at least two digital signals, To continue doing this, Otherwise, if a threshold is exceeded, the method includes the step of deactivating all pixels in the array until it is desired to reactivate them to sense incident photons again.

[0053] In one embodiment, the method further includes the step of generating a digital signal indicating the detection of an event when a user-defined time synchronization threshold for photons is reached.

[0054] In one embodiment, the method further includes the step of sending the address of the triggered pixel to a common address line when an event detection signal is generated and while the pixel is deactivated.

[0055] In one embodiment, the method is applied to a mother array that is divided into arrays, and the following steps are performed in parallel for all arrays into which the mother array is divided: - A step of generating at least one digital signal in response to a photon collision with one or more pixels of at least one pixel array, - A step of converting the digital signal coming from each pixel into a corresponding analog signal that is quantized by amplitude and duration, - The analog adder node adds analog signals together to obtain an analog total signal; - A step of converting the output signal of an analog adder node into at least two digital signals, Includes, At least two output digital signals from the array are transmitted to subsequent arrays in a seamless cascaded configuration until the mother array ends. At least one high logic digital output signal from the mother array is sent to an output block, which generates an event digital signal when it reaches a user-defined time-constant count photon threshold.

[0056] Further features and advantages of the present invention will become clearer from the description of the accompanying drawings. [Brief explanation of the drawing]

[0057] The present invention is provided as a non-limiting example and is described below with reference to specific examples shown in the accompanying drawings. These drawings illustrate various aspects and embodiments of the present invention, and reference numerals indicating structures, components, materials and / or similar elements in the various drawings are indicated by similar reference numerals where applicable.

[0058] [Figure 1] Figure 1 and a portion of it, Figure 1A, schematically show the array of a conventional all-digital SPAD photodetector and the configuration of each pixel in the detailed array, respectively. [Figure 2] Figure 2 and a portion of it, Figure 2A, schematically show a conventional all-analog SiPM photodetector and the configuration of each microcell in a detailed array, respectively. [Figure 3] Figure 3 and a portion thereof, Figure 3A, schematically show the photon event detection system according to the present invention and the configuration of each pixel in the detailed array, respectively. [Figure 4] Figure 4 shows a circuit diagram of a hypothetical embodiment of an event electronic device for detecting events in the system shown in Figure 3. [Figure 5] Figure 5 shows a schematic diagram of the modularization of the system into an array and the repetition of event detection electronics up to the mother array level according to the present invention. [Figure 6] Figure 6 shows a schematic diagram of a hypothetical modular structure of a system for detecting photon events according to the present invention, along with a circuit diagram of the basic block or array. [Figure 7] Figure 7 shows a schematic diagram of the routing of event detection electronics by H-tree fractal recursive branching in the modular array partitioning of the photon event detection system shown in Figure 5. [Figure 8] Figure 8 schematically shows an event-driven readout electronic device according to the present invention. [Figure 9] Figure 9 shows a flowchart of the steps of the method for detecting photon events according to the present invention in the case of a single-pixel array system. [Figure 10] Figure 10 shows a flowchart of the steps of the method for detecting photon events according to the present invention in the case of a system having a modular array structure. [Modes for carrying out the invention]

[0059] While various modifications and alternative configurations are possible for this invention, several embodiments provided for illustrative purposes are described in detail below.

[0060] In all cases, it should be understood that the present invention is not intended to be limited to the specific embodiments described, but rather, it is intended to encompass all modifications, alternatives, and equivalent structures that fall within the scope of the invention as described in the claims.

[0061] Therefore, in the following explanation, the use of "e.g.," "etc.," and "or" indicates unrestricted, non-exclusive alternatives unless otherwise indicated. The use of "also" means "including, but not limited to," unless otherwise indicated. The use of "include / comprise" means "including / comprise, but not limited to," unless otherwise indicated.

[0062] Referring to Figure 1, an array of SPAD photodetectors using conventional technology is shown.

[0063] The array indicated by reference numeral 1 comprises a number of independent pixels 2. Each pixel 2 comprises a SPAD photodetector 3, a front-end electronic device 4, and a processing electronic device consisting of, for example, a time-to-digital converter (TDC) 5 configured to measure the arrival time of photons F on each SPAD 3.

[0064] As described above, when a photon F collides with the SPAD, an electron-hole pair is generated, which causes an avalanche multiplication of the charge and generates a macroscopic current. This current is converted into a digital signal by the front-end electronics 4. Thus, each pixel 2 is a digital output Ud1...Ud indicating the arrival time of the photon F at the SPAD 3. b (b indicates the number of bits in the digital output) generates digital output Ud1…Ud b This is sent to the bus located at the output of array 1.

[0065] Instead, Figure 2 shows a conventional SiPM photodetector.

[0066] Generally, the SiPM photodetector, indicated by reference numeral 6, comprises an array of microcells 7. Each microcell 7 has a quenching resistor R that is completely similar to the SPAD photodetector 8 described above with reference to array 1. Q It is provided in series with the quenching resistor R, and its function is, as described above, to stop the avalanche multiplication generated by electron-hole pairs produced when a photon collides with the SPAD8 of the microcell 7, and to allow the microcell 7 to detect new incident photons. Q It is connected between each SPAD8 and the common node 9, and the common node 9 acts as a single shared adder node for all SPAD8s. Thus, the output of SiPM6 is the output analog current Ua1, ..., Ua of all microcells 7 struck by the photon F. x Analog total sum Ua tot This is the result.

[0067] Referring to Figure 3, a system for detecting photon events according to a preferred embodiment of the present invention is shown.

[0068] Generally, the system indicated by reference numeral 100 comprises an array M of pixels 10, each pixel including a photodetector 12, preferably a SPAD, a front-end electronics unit 14, and an event-driven readout electronics unit 15 configured to provide information about the spatial position of the pixel triggered by the photons of the array, as will be described in more detail below.

[0069] The following discussion will focus on SPAD photodetectors, but it should be understood that the information provided can be applied to other types of photodetectors, as long as they are suitable for the purpose. For example, as an alternative to SPADs, an analog photodetector (also known as a linear detector) can be used after digitizing the output information.

[0070] Each pixel 10 that the SPAD12 is hit by photon F outputs digital signals Sd1, ..., Sd x (where x indicates the number of SPADs present in array M), and the addresses Ip1, ..., Ip b (where b indicates the number of bits of the address) of the hit pixel 10. The said address is transmitted to address line L (see Fig. 8).

[0071] As will be described in detail below, the output of system 100 is a number of digital signals for the detection of single photon events and the time coincidence counting of two or more photons, and preferably provides, on address line L, the addresses of pixels triggered within a predefined time window of preferably about a few nanoseconds.

[0072] System 100 also includes event detection electronics 20 configured to detect time coincidence events of two or more photons and on-chip single photon events distributed across the entire array M within the time coincidence counting window, as will be described in detail below. The number of time coincidence photons detected by system 100 can be set by the user at any time.

[0073] Event detection electronics 20 essentially constitutes detector nodes shared among the pixels 10 of array M, and identifies when photon F (single photon event) or multiple photons F (time coincidence event of multiple photons) respectively drove one or more SPAD12s, and as a result, the respective output digital signals Sd1, ..., Sd x of each pixel 10 are generated.

[0074] The triggered SPAD12 can be anywhere within array M, whereby the detection of time coincidence events of photon F occurs indiscriminately across the entire array M, and thus is not limited to adjacent pixels 10, a part of array M, or any arbitrarily assumed group of pixels 10.

[0075] As shown in detail in Figure 4, the event detection electronic device 20 comprises a plurality of digital-to-analog (D / A) converters 21 connected in parallel to each other, one for each pixel 10 of the array M, an analog adder node 22 operably connected to the plurality of digital-to-analog converters 21, and a combined analog-to-digital (A / D) converter 24 operably connected to the analog adder node 22.

[0076] Photon F collides with SPAD12 at the output digital signals Sd1, ..., Sd of the digital front-end electronic device 14 of pixel 10. x These are the respective quantized analog signals Sa1, ..., Sa x The output is provided as input to each of the multiple digital-to-analog converters 21, for example, to a voltage-controlled current generator (i.e., a MOS transistor).

[0077] Unlike the known types of SiPM photodetectors described above (see Figure 2), the quantized analog signals Sa1, ..., Sa x This is a clearly defined signal with adjustable duration and amplitude, rather than the current generated by SPAD12. This has the advantage of maintaining immunity to the readout noise inherent in the SPAD photodetector array, as explained with reference to Figure 1, by allowing the signal amplitude to be set well above the electronic noise limit.

[0078] Quantized output analog signals Sa1, ..., Sa of the digital-to-analog converter 21 x This is the feedback resistor R f Provided as input to an analog adder node 22 having an operational amplifier 23, preferably in the form of a transimpedance amplifier (TIA), which includes an operational amplifier 23 equipped with a single quantized analog signal Sa1, ..., Sa from a digital-to-analog converter 21. x These are added at analog adder node 22 to produce a similarly quantized analog sum signal Sa.

[0079] The duration of the same clock window is determined by signals Sd1, ..., Sd x The (programmable) duration of Sa1, ..., Sa x The (programmable) duration is consistent with, and preferably on the order of a few nanoseconds. Only photons detected simultaneously within the same-counting window can be detected as a multi-photon time-coincident event, with signals Sa1, ..., Sa totaling Sa. x This is the result.

[0080] Digital signals Sd1, ..., Sd x The duration of the quantized analog signals Sa1, ..., Sa x When the duration of the time synchronization window, and correspondingly the duration of the time synchronization window, are adjusted according to the amplitude of the analog sum signal Sa at the analog adder node 22, it becomes possible to distinguish the number of pixels 10 that are triggered simultaneously within the time synchronization window.

[0081] For this purpose, the total analog signal Sa is converted to an output analog signal Sout by a transimpedance amplifier TIA, and the output analog signal Sout is input to the combined analog-to-digital converter 24.

[0082] Specifically, the integrated analog-to-digital converter 24 includes a first comparator 25 and a second comparator 26 configured to identify the number of photon events in accordance with the amplitude of the total analog signal Sa, and therefore within the corresponding time synchronization window.

[0083] More specifically, the first comparator 25 has a first threshold TH1 that corresponds to the simultaneous triggering of a number N of pixels 10 greater than or equal to a first value, where N≧1 in the illustrated example, while the second comparator 26 has a second threshold TH2 that corresponds to the simultaneous triggering of a number N of pixels greater than or equal to a second predetermined value, where N≧2 in the illustrated example.

[0084] The output analog signal Sout from the analog adder node 22 is compared with the first threshold TH1 and the second threshold TH2 in the first comparator 25 and the second comparator 26, respectively.

[0085] Therefore, if Sout > TH1, i.e., if the output analog signal Sout of the transimpedance amplifier TIA exceeds the first threshold TH1, this corresponds to a simultaneous trigger of one or more pixels 10, and the first comparator 25 indicates at least one photon event within the time coincidence counting window, the digital signal Sd 1F The output is Sout > TH2, i.e., the output analog signal Sout of the transimpedance amplifier TIA also exceeds the second threshold TH2, which corresponds to the simultaneous triggering of two or more pixels 10, and the second comparator 26 indicates a high logic value digital signal Sd, which represents a time-coincidence event of at least two photons within the time-coincidence window. 2F Outputs.

[0086] In other words, if the output analog signal Sout exceeds the first threshold TH1 but does not exceed the threshold TH2, then a single digital signal Sd indicates a single-photon event. 1F Only is generated, but if the output analog signal Sout exceeds both the first threshold TH1 and the second threshold TH2, the digital signals Sd1, ..., Sd generated by pixel 10 indicate at least two photon coincidence counting events. x Two signals Sd having the same duration 1F , Sd 2F This is generated. The output digital signal of system 100 is the digital event signal Sd set by the user. event The digital event signal Sd corresponds to the exceedance of the first threshold TH1 (detection of at least one photon event) or the exceedance of the second threshold TH2 (detection of at least two photon time-coincidence events). event This is generated by output block 28 (see Figure 7).

[0087] Although two comparators are shown in the illustrated embodiment, the event detection electronic device 20 may have more than two comparators, each comparator having a maximum TH nThe threshold increases up to n, where n is the number of concurrently counted photons to be detected (in a hypothetical embodiment, the threshold includes all values ​​between 1 and n), and is within the scope of protection of the present invention. In this case as well, the output digital signal of system 100 corresponds to the exceedance of the user-set threshold. Naturally, this leads to an increase in the occupancy of the inactive region of array M and an increase in energy consumption.

[0088] Figures 5 to 7 show a modular and scalable system 100 for detecting photon events. In this system, the system 100 comprises a mother array MM divided into multiple arrays M, each array M being equipped with its own event detection electronic equipment 20, which are seamlessly connected to each other in a cascaded configuration.

[0089] More specifically, referring to Figure 5, the array M of the mother array MM corresponds to the digital signals Sd1, ..., Sd x These signals are generated and sent as input to each event detection electronic device 20. Within each event detection electronic device 20, the digital signals Sd1, ..., Sd x The analog signals Sa1, ..., Sa are transmitted by the digital-to-analog converter 21. x These signals are converted and added at each analog adder node 22. The output analog signal S of each analog adder node 22 out The signals are sent as input to each integrated analog-to-digital converter 24, which then receives a number of digital signals Sd 1F ,...,Sd yF The system outputs (where y represents the number of output signals generated), each corresponding to the threshold exceedance of each comparator of the integrated analog-to-digital converter 24. For the threshold to be exceeded, triggers must occur simultaneously. That is, the triggers must occur within a user-defined time window, the duration of which corresponds to the digital signals Sd1, ..., Sd x The duration of the analog signals Sa1, ..., Sa xThis matches the duration.

[0090] Output digital signal Sd of each event detection electronic device 20 1F ,...,Sd yF The data is then cascaded as input to another event detection electronic device 20 until the mother array MM finishes.

[0091] At the end of the cascaded connection of the event detection electronic device 20, the output block 28 outputs a digital event signal Sd when an event occurs. event This generates at least TH across the entire mother array MM. tot It is understood that this reaches a number of photons in a single simultaneous clock, and here TH tot This is a threshold corresponding to the number of time-coordinated photons set by the user. The output block may be implemented by a multiplexer 28 that selects the correct output signal of the last event detection electronic device 20 in the cascaded connection. As an example, the output signal Sd of the multiplexer 28 event This may be a signal corresponding to the exceedance of the first threshold TH1 (detection of at least one photon event) or a signal corresponding to the exceedance of the second threshold TH2 (detection of at least two time-coincidentally counted photon events).

[0092] Particularly preferred embodiments of the modular and scalable system 100 are shown in Figures 6 and 7.

[0093] System 100 comprises a 96x96 pixel mother array MM, preferably made using CMOS technology. The number of pixels in the mother array MM was selected to have the maximum number of SPADs 12 while ensuring good performance of the electronics of System 100. Of course, the following description regarding the 96x96 pixel mother array MM also applies to mother arrays of different sizes.

[0094] Next, the mother array MM is a 12x12 pixel array M 12 It was divided into. Each array M 12Pixel 10 is connected to each event detection electronic device 20 of the type described above and with reference to Figure 4.

[0095] Therefore, each array M 12 The event electronic equipment 20 is array M 12 Multiple digital-to-analog converters 21, one for each pixel 10, and array M 12 It comprises an analog adder node 22 common to all pixels 10, and a combined analog-to-digital converter 24 operably connected to the analog adder node 22. Of course, the mother array MM can be divided into arrays M having different numbers of pixels.

[0096] As mentioned above, each array M of the mother array MM 12 The event detection electronic device 20 receives the output digital signals Sd1, ..., Sd of the pixel 10 struck by the photon through each digital-to-analog converter 21. x The amplitude and intensity are quantized corresponding analog signals Sa1, ..., Sa x (Its duration determines the duration of the time synchronization window) can be converted to the quantized analog signals Sa1, ..., Sa x These are added at analog adder node 22 to obtain the analog total signal Sa. The analog total signal Sa is then output as the analog signal S out It will be converted.

[0097] Then, the final analog-to-digital conversion is performed in the integrated analog-to-digital converter 24, and a number of high logic value digital signals Sd correspond to the exceedance of the threshold of each of the 1, 2, ..., n comparators of the analog-to-digital converter 24 within the time synchronization window. 1F ,...,Sd yF This is generated.

[0098] In the analog adder node 22, all quantized analog signals Sa1, ..., Sa xTo add these, a digital-to-analog converter 21 (which may be implemented using, for example, a voltage-controlled current generator) is connected in parallel, and thus generates a signal proportional to the number of interconnected generators.

[0099] Furthermore, array M 12 The magnitude of this is the parasitic capacitance C at adder node 22. par However, the total analog signal Sa and the output analog signal S out The parameters are selected to be small enough to enable high-speed electronic processing and fast rising / falling edges. In this way, timing information, i.e., the duration of the time concurrency window and the point in time when the threshold of the analog-to-digital converter 24 is exceeded, is not lost.

[0100] As described above, the arrays constituting the mother array MM can be connected to each other in such a way that each event detection electronic device 20 is connected in an operable manner through a seamless cascaded configuration.

[0101] As a non-limiting example, as shown in Figure 7, the aforementioned 12x12 pixel array M 12 Referring to the 96x96 pixel mother array MM which is divided into four 12x12 pixel arrays M 12 Digital signal Sd 1F ,...,Sd yF This is an array of four 12x12 pixels M 12 A 24x24 pixel array M resulting from the sum of 24 For the detection of the event, it may be added at the analog adder node 22 of the electronic device 20.

[0102] In a completely similar manner, four array M 24 Digital signal Sd 1F ,...,Sd yF This is an array of four 24x24 pixels M 24 A 48x48 pixel array M resulting from the sum of 48To detect the event, the electronic device 20 may be added at the analog adder node 22, and to detect the event in the mother array MM, the electronic device 20 located at the center of the mother array MM in Figure 7 is used.

[0103] Finally, the event detection electronic equipment 20 of the array mother MM is operably connected to the multiplexer 28, which consists of, for example, TH1, TH2, ...TH n A threshold TH set by the user is selected from among the following. tot When a large number of simultaneously counted photons are detected within a time window equal to the digital event signal Sd event Outputs.

[0104] The selection of these pixel counts is based on the array M (in this example, array M 12 This is the result of adjusting between the leakage current and parasitic capacitance issues in the ) and the total number of stages in the digital-to-analog and analog-to-digital cascade conversions, thereby enabling the event and the corresponding output signal Sd event A delay occurs between the generation of and the output, and this is a function of the number of stages.

[0105] Specifically, in order to minimize mismatches and delays in signal propagation between arrays M of the mother array MM of system 100, routing with H-tree fractal recursive branching was implemented for seamless cascading connections between event detection electronic devices 20 of array M.

[0106] Such H-tree fractal recursive branching is clearly shown in Figure 7, with each 12x12 pixel array M 12 The event detection electronic device 20 has a 12x12 pixel array M 12 It is positioned in the center, and similarly, each 24x24 pixel array M 24 The event detection electronic device 20 uses a 24x24 pixel array M 24 Located in the center, each 48x48 pixel array M 48 The event detection electronic device 20 has an array M with each 48x48 pixels. 48It is positioned in the center, and the same applies to the following.

[0107] In this way, all paths connecting each event detection electronic device 20 to subsequent event detection electronic devices 20 can be made identical, which has the advantage of not being affected by different time delays (skew). In fact, the H-tree shape equalizes the paths from the output of each integrated analog-to-digital converter 24 (wherever it is located) to the input of the digital-to-analog converter 21 of the electronic device 20 for the detection of cascaded events.

[0108] The signal propagating along the branches of the H-tree is the output digital signal of the comparator of the integrated analog-to-digital converter 24. This makes it possible to suitably propagate only the digital signal, which is less susceptible to the effects of electronic noise, along a long path (resistively and capacitively).

[0109] When an event detection electronic device 20 of array M, or in the case of a modular and scalable system 100, a cascade of event detection electronic devices 20 of array M into which the mother array MM is divided, detects at least one photon event or two or more photon time-simultaneous counting events, only the pixel 10 struck by the photon F transmits its address. This has the advantage of providing only the spatial coordinates of the triggered pixel without wasting resources on unnecessary data.

[0110] For this purpose, as shown in detail in Figure 8, all pixels 10 of array M, or in the case of a modular and scalable system 100, of array M from which the mother array MM has been divided, are connected to a shared address line L.

[0111] As a non-exclusive example, communication of pixel 10 on address line L is via CAN (Controller Area Network) or I 2It can be based on a "zero-win" serial communication protocol similar to the C (Inter-Integrated Circuit) serial bus communication protocol. Specifically, the triggered pixel 10 with the lowest address controls address line L first and outputs its address. The other triggered pixels 10 are queued and control address line L in turn.

[0112] Each pixel 10's read electronic device 15 comprises three main blocks: a pixel state sampling block 16, an address writing block 17, and a block 18 that monitors the state of the address line L, all of which are global R pull-up It communicates with an open-drain (or open-collector) serial port 19 equipped with a resistor. The open-drain solution works as follows: when one of the pixels 10 conducts its output, it sets address line L to a low level (logic level 0), and when the output becomes inactive, address line L is pulled up by a global pull-up resistor R pull-up This returns it to a high level (logical level 1).

[0113] The sampling block 16 preferably includes a sampler with a 1-bit register and is configured to sample the state of the pixel 10, i.e., whether or not the pixel 10 is triggered.

[0114] The write block 17 preferably includes, for example, a 10-bit shift register, and the addresses Ip1, ..., Ip of the pixel 10 triggered on the address line L b It is configured to write serially.

[0115] The monitoring block 18 preferably consists of a finite state machine that monitors the state of address line L, where address line L is another triggered pixel 10 address Ip1, ..., Ip b If the system is busy writing, the writing process will be interrupted and repeated in subsequent data transfers.

[0116] Specifically, each pixel 10 activates the open-drain serial port 19 when it needs to communicate a bit equal to 0 at its address, and leaves the open-drain serial port 19 inactive when it needs to communicate a bit equal to 1 instead, and the global pull-up resistor R pull-up This sets address line L to 1. If, while pixel 10 is communicating 1, another pixel 10 communicates 0 (by activating the open-drain serial port 19), the first pixel, i.e., the pixel communicating 1, recognizes that address line L has been changed to 0 by the other pixel 10, and communication at that address is stopped. As a result, the second pixel 10, i.e., the pixel 10 that communicated 0, takes over address line L on its own without its address being changed in any way by the first pixel 10.

[0117] In the case of a modular and scalable system 100, the option of dividing the mother array MM into array M (for example, a 24x24 pixel array, which does not necessarily correspond to the size of array M defined for event detection purposes) for read purposes preferably allows the shared data lines to be set to logical level 1 or logical level 0 within the time it is possible to communicate addresses at a specific clock frequency, while using small transistors.

[0118] The system 100 according to the present invention is configured to communicate n+1 addresses, that is, a number of addresses equal to the number of concurrently counted photons F within the time window that the user wants to detect plus 1, so that in a later step, it can be identified whether the event is exactly a concurrently counted event of n photons (in which case there are only n valid addresses) or a concurrently counted event of more than n photons (in which case there are n+1 valid addresses).

[0119] For example, if a user wants to know the time coincidence of two photons, the system communicates three addresses on address line L. In practice, to detect the position of a pair of time coincidence photons F, considering the low proportion of coincidence photons, in principle two addresses Ip1,...,Ip b While one address is sufficient, it is preferable to have two or more addresses, for example three, given the high expected proportion of spurious photons, for example, from ambient light or events triggered without incident light. This is to verify whether the measurement is invalidated by spurious events. In other words, the measurement is valid only if the third address corresponds to a value that cannot be expected for any pixel address (i.e., it is not a valid address), which means that no spurious third event has occurred within the time synchronization window.

[0120] Assuming a 100MHz reference clock, the transfer of address data from array M, or from each array M (in the case of a modular and scalable system 100, from the mother array MM to which the mother array MM is divided) to the final memory bank from which the data is read, takes approximately 330ns (considering a 10-bit address). During this period, the array of array M or the mother array MM is inactive, and this is called the so-called "dead time". In other words, all SPAD12 of pixel 10 are deactivated and cannot detect new incident photons F. This is a significant improvement over the "dead time" of reading the array with a standard approach that consists of communicating the state of each pixel (using a single bit indicating active and inactive, where 1 is active and 0 is inactive). As an example, consider a 96x96 pixel array M 96 And with a 100MHz reference clock, scanning the entire array would take 92,600ns.

[0121] A method for detecting photons according to a preferred embodiment of the present invention will be described with reference to Figure 9. This method is performed using the single-array detection system 100 described above with reference to Figures 3, 4, and 8.

[0122] This method starts at step 200, where pixel 10 of array M is selectively activated, i.e., the pixel is made capable of selectively detecting photons.

[0123] Thus, the method includes a series of steps 201, 202, 203, 204, 205, which are executed continuously each time a pixel is triggered until the pixel is deactivated in the next step 206, or can be executed in parallel by various pixels.

[0124] Next, the method proceeds from step 200 to step 201, during which n digital signals Sd1,..., Sd equal to the number of pixels 10 of array M that photons F have collided with are generated. x are generated.

[0125] From step 201, the method proceeds as follows. - Proceed to step 202, where the output digital signals Sd1,..., Sd of array M are input into the corresponding digital - analog converters 21 of the event detection electronics 20 of array M, and these signals are converted into the corresponding quantized analog signals Sa1,..., Sa. x are input into the corresponding digital - analog converters 21 of the event detection electronics 20 of array M, and these signals are converted into the corresponding quantized analog signals Sa1,..., Sa. x are converted. - Proceed from step 202 to step 203, where the quantized output analog signals Sa1,..., Sa of the digital - analog converters 21 are input into the analog adder node 22 of the event detection electronics 20 of array M, and these signals are added to obtain an analog total signal Sa, which is also quantized. x are input into the analog adder node 22 of the event detection electronics 20 of array M, and these signals are added to obtain an analog total signal Sa, which is also quantized. - Proceed from step 203 to step 204, where the output analog signal S of the analog adder node 22 is converted by the integrated analog - digital converter 24 into a number of digital signals Sd corresponding to the excess of each threshold (e.g., by 1 photon,..., n photons). out are input into the analog adder node 22 of the event detection electronics 20 of array M, and these signals are added to obtain an analog total signal Sa, which is also quantized. 1F ,..., Sd yF are converted.

[0126] Specifically, the step of analog-digital conversion of the output analog signal S of the analog adder node 22 out comprises comparing the output analog signal S out with at least a first threshold TH1, for example TH1 corresponding to the trigger of N pixels 10 greater than or equal to 1, a second threshold TH2 corresponding to the trigger of N pixels 10 greater than or equal to 2 within the same counting time window, and with a first comparator 25 and a second comparator 26 of the general analog-digital converter 24 of the event detection electronic device 20, respectively.

[0127] The method proceeds to step 205, checks whether the threshold set by the user is exceeded, and if so (step 205: YES), the method proceeds to step 206, where the pixels 10 of the array M are deactivated, i.e., they are no longer affected by incident photons, and the parallel execution from steps 201 to 205 is interrupted. Otherwise (step 205: NO), the execution of steps 201 to 205 of the method continues.

[0128] The method proceeds from step 206 to step 207, and an event signaling Sd tot corresponding to the detection of a number of photons equal to the threshold TH event set by the user within the time coincidence window is generated as a digital signal.

[0129] The method proceeds from step 207 to step 208, and the triggered pixels 10 transmit their own addresses to the common address line L.

[0130] The method returns from step 208 to step 200, and all the pixels 10 of the array M are reactivated.

[0131] Referring to FIG. 10, a method for detecting photons according to an alternative embodiment of the present invention will be described. The method is executed using the modular and scalable version of the detection system 100 described above and with reference to FIGS. 5 to 8.

[0132] The process begins with step 300, in which pixel 10 of the mother array MM is selectively activated.

[0133] Therefore, the method provides a series of steps 301, 302, 303, 304, 305 which provide each array M obtained by dividing the mother array MM (in Figure 10, each array is shown by the juxtaposition of identical concatenated blocks) and proceed with processing in a cascade until the mother array MM is finished, these steps are performed continuously whenever a pixel is triggered and may be performed in parallel by various pixels until the pixel is deactivated in the next step 306.

[0134] The method proceeds from step 300 to step 301, during which time n digital signals Sd1, ..., Sd are generated, equal to the number of SPAD12s in array M where the photon F collides. x This is generated, and as a result, each pixel 10 is triggered.

[0135] From step 301, the method proceeds as follows: - Proceed to step 302, output digital signals Sd1, ..., Sd x These signals are input to the corresponding digital-to-analog converter 21 of the event detection electronic device 20 of array M, and these signals are the corresponding quantized analog signals Sa1, ..., Sa x It will be converted. - Proceed from step 302 to step 303, quantized output analog signals Sa1, ..., Sa of the digital-to-analog converter 21. x These signals are input to the analog adder node 22 of the event detection electronic device 20 of array M, where they are added together to obtain an analog total signal Sa, which is also quantized. - Proceed from step 303 to step 304, and the output analog signal S of the analog adder node 22 out The integrated analog-to-digital converter 24 converts numerous digital signals Sd corresponding to the exceedance of each threshold. 1F ,...,Sd yF It will be converted.

[0136] Specifically, the output analog signal S of the analog adder node 22 out The analog-to-digital conversion step involves outputting an analog signal S out This involves comparing the data with at least a first threshold TH1, for example, TH1 corresponding to the triggers of 1 or more N pixels 10, a second threshold TH2 corresponding to the triggers of 2 or more N pixels 10 within the same time interval window, and the first comparator 25 and second comparator 26 of the integrated analog-to-digital converter 24 of the event detection electronic device 20.

[0137] The method proceeds to step 305 to check if the threshold set by the user has been exceeded. If it has been exceeded (step 305: YES), the method proceeds to step 306, where pixel 10 of the mother array MM is deactivated and the parallel execution of steps 301 through 305 is interrupted. Otherwise (step 305: NO), the execution of steps 301 through 305 continues.

[0138] The method proceeds from step 306 to step 307, where the user-defined threshold TH is set within the time synchronization window. tot Event signaling Sd corresponds to the detection of a number of photons equal to . event A digital signal is generated.

[0139] The method proceeds from step 307 to step 308, where the triggered pixel 10 transmits its own address to the common address line L.

[0140] The method involves returning from step 308 to step 300, and pixel 10 of the mother array MM is reactivated.

[0141] From the above explanation, it is clear that the proposed system and method for detecting the aforementioned photons can achieve the proposed objectives.

[0142] Therefore, it will be apparent to those skilled in the art that modifications and variations can be made to the solution described with reference to the drawings without exceeding the scope of protection of the present invention as defined by the attached claims.

Claims

1. A system (100) for detecting photon (F) events, comprising at least one array (M;MM) of pixels (10), each pixel (10) being a photodetector (12) and a digital signal (Sd １ , . . , Sd ｘ The system includes a front-end electronic device (14) that outputs a signal. The system comprises at least one event detection electronic device (20), and the at least one event detection electronic device (20) is - A plurality of digital-to-analog converters (21), one for each pixel (10) of the array (M;MM), wherein each plurality of digital-to-analog converters (21) receives the digital signal (Sd) coming from each of the pixels (10). １ , . . , Sd ｘ ) corresponds to the analog signal (Sa １ , . . , Sa ｘ It is configured to convert to the corresponding analog signal (Sa １ , . . , Sa ｘ ) comprises multiple digital-to-analog converters (21) that are quantized by amplitude and duration, - An analog adder node (22) to which the plurality of digital-to-analog converters (21) are operably connected, wherein the analog adder node (22) receives the quantized analog signals (Sa １ ,..., Sa ｘ ) from the digital-to-analog converters (21) and is configured to add them to obtain a total analog signal (Sa); an analog adder node (22). - A combined analog-to-digital converter (24) comprising at least one first comparator (25) and a second comparator (26) operably connected to the analog adder node (22), Equipped with, The first comparator (25) receives the output signal (S) of the analog adder node (22). ｏｕｔ ) is a first threshold (TH) corresponding to the trigger of the number of pixels in the time synchronization window that is greater than or equal to a first predetermined value. １ It is configured to be compared with, The second comparator (26) receives the output signal (S) of the analog adder node (22). ｏｕｔ ) is a second threshold (TH) corresponding to the trigger of the number of pixels in the time synchronization window that is greater than or equal to a second predetermined value. ２ It is configured to be compared with, The first comparator (25) and the second comparator (26) enable event detection when the number of incident photons to the array (M;MM) within the time synchronization window exceeds the first predetermined value or the second predetermined value, by adjusting the output signal (S) of the analog adder node. ｏｕｔ ) each of the first thresholds (TH １ ) or the second threshold (TH ２ When it exceeds ), the digital signal (SD １Ｆ , . . , Sd ｙＦ It is configured to output ) The aforementioned system, An output block (28) is configured to generate a digital event signal (Sd event) when a user-defined threshold (TH tot) of time-coordinated photons (F) is reached, A mother array (MM) divided into arrays (M), The array (M) is further comprising the event detection electronic devices (20) of the array (M) which are connected to each other in a seamless cascaded connection, and the last event detection electronic device (20) in the cascaded connection is connected to the output block (28). System (100).

2. The first threshold (TH １ ) corresponds to a trigger of one or more pixels (10), and the second threshold (TH ２ The system (100) according to claim 1, wherein the trigger corresponds to a number of pixels (10) of two or more.

3. Each pixel (10) of the array (M;MM) receives the digital event signal (Sd ｅｖｅｎｔ When generating the triggered pixel (10), the address (Ip １ , . . , IP ｂ The system (100) according to claim 1 or 2, comprising an event-driven read electronic device (15) configured to transmit to a common address line (L).

4. Each pixel (10) of the event-driven reading electronic device (15) comprises a pixel state sampling block (16), an address writing block (17), and a block (18) that monitors the state of the common address line (L), wherein the pixel state sampling block (16), the address writing block (17), and the block (18) are connected by a global pull-up resistor (R ｐｕｌｌ－ｕｐ The system (100) according to claim 3, which communicates with an open-drain serial port (19) having ).

5. The cascaded connection of the event detection electronic devices (20) of the array (M) is followed by a path having an H-tree fractal recursive branch, according to any one of claims 1 to 4, the system (100).

6. The system (100) according to any one of claims 1 to 5, wherein the photodetector (12) of each pixel (10) is a SPAD.

7. A method for detecting a photon event, the method comprising the following steps performed in parallel: - At least one digital signal (Sd) in response to a photon collision with one or more pixels (10) of at least one pixel array (M;MM) １ , . . , Sd ｘ The steps of generating (201; 301) - The digital signal (Sd) coming from each triggered pixel １ , . . , Sd ｘ ) corresponds to analog signals (Sa １ , . . , Sa ｘ A step (202; 302) of converting to the corresponding analog signal (Sa １ , . . , Sa ｘ ) is quantized by amplitude and duration, a transformation step (202; 302), Addition step (203; 303), wherein the analog adder node (22) quantizes the analog signal (Sa １ , . . , Sa ｘ The steps (203; 303) involve adding the values ​​and obtaining an analog total signal (Sa), When the analog signal exceeds the two thresholds, the output signal (S) of the analog adder node (22) ｏｕｔ ) to two digital signals (SD １Ｆ , . . , Sd ｙＦ The steps to convert to (204;304), Includes, The analog-to-digital conversion step (204; 304) includes at least the following steps: - The output signal (S) of the analog adder node (22) ｏｕｔ ) is a first threshold (TH) corresponding to the trigger of the number of pixels in the time synchronization window that is greater than or equal to a first predetermined value. １ The step of comparing with ) - The output signal (S) of the analog adder node ｏｕｔ ) is a second threshold (TH) corresponding to the trigger of the number of pixels in the time synchronization window that is greater than or equal to a second predetermined value. ２ The step of comparing with ) - When the number of photons incident on the array (M;MM) within the time synchronization window exceeds the first predetermined value or the second predetermined value, an event detection is enabled, and when the output signal of the analog adder node (22) exceeds the first threshold or the second threshold, a digital signal (Sd １Ｆ , . . , Sd ｙＦ The steps to generate ) and Includes, The method further includes an initial step (200;300) of selectively activating the pixels (10) of the array (M:MM) to sense incident photons, The method described above includes the step (205; 305) of confirming that a threshold (TH1, ..., THn) set by the user has been exceeded, If the threshold (TH 1, ..., TH n) is not exceeded (205: NO; 305: NO), then the following steps are taken. - A step (201; 301) of generating at least one digital signal (Sd 1, ... Sd x) in response to a collision of a photon (F) with one or more pixels (10) of at least one pixel array (M; MM), - A conversion step (202; 302) comprising converting the digital signals (Sd 1, ... Sd x) coming from each pixel to corresponding analog signals (Sa 1, ... Sa x), wherein the corresponding analog signals (Sa 1, ... Sa x) are quantized by amplitude and duration, - Addition step (203; 303), wherein the quantized analog signals (Sa 1, ... Sa x) are added at the analog adder node (22) to obtain an analog total signal (Sa), - Steps (204; 304) of converting the output signal (S out) of the analog adder node (22) into two digital signals (Sd 1F, ..., Sd yF), To continue doing this, If the threshold (TH 1, ..., TH n) is exceeded (205: YES; 305: YES), the step (206; 306) is to deactivate the pixel (10) of the array (M; MM), Methods that further include this.

8. The first threshold (TH １ ) corresponds to a trigger of one or more pixels (10), and the second threshold (TH ２ The method according to claim 7, wherein the trigger corresponds to a number of pixels (10) of two or more.

9. User-defined time synchronization threshold (TH ｔｏｔ When it reaches ) a digital event signal (Sd ｅｖｅｎｔ The method according to claim 7 or 8, further comprising the step of generating (207; 307).

10. The aforementioned digital event signal (Sd ｅｖｅｎｔ When generating the triggered pixel (10), the address (I ｐ１ , . . . , I Ｐｂ The method according to claim 9, further comprising the step (208; 308) of transmitting to a common address line (L).

11. - At least one digital signal (Sd) in response to a collision of a photon (F) with one or more pixels (10) of at least one pixel array (M;MM) １ , . . . Sd ｘ The steps of generating (301) and - A conversion step (302) wherein the digital signal (Sd) coming from each triggered pixel １ , . . . Sd ｘ ) corresponds to analog signals (Sa １ , . . . Sa ｘ Converts to the corresponding analog signal (Sa １ , . . . Sa ｘ ) is quantized by amplitude and duration, a transformation step (302), - An addition step (303) in which the quantized analog signal (Sa) is added at the analog adder node (22) １ , . . . Sa ｘ The steps include adding (303) to obtain an analog total signal (Sa), - Output signal (S) of the analog adder node (22) ｏｕｔ ) to two digital signals (SD １Ｆ , . . , Sd ｙＦ The step of converting to (304), The steps, including the above, are repeated for all arrays (M) into which the mother array (MM) is divided. The two digital signals (Sd) of the array (M) １Ｆ , . . , Sd ｙＦ ) is transmitted to subsequent arrays (M) in a seamless cascaded configuration until the mother array (MM) is finished. The two digital signals (Sd) of the mother array (MM) １Ｆ , . . , Sd ｙＦ ) is transmitted to the output block (28), and the output block (28) receives the time-coincident counting photon (F) threshold (TH) set by the user. ｔｏｔ When it reaches ) a digital event signal (Sd ｅｖｅｎｔ ) generate The method according to any one of claims 7 to 10.

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