Photon counting circuit system and photon counting method

Abstract

The present disclosure generally relates to a photon counting circuitry (11) configured to: determine whether there is a signal coincidence of at least two pixel signals (CLK1, CLK2) based on a degree of overlap in time of the at least two pixel signals (CLK1, CLK2) of the at least two pixels (SPAD1, SPAD2) of a photon counting time-of-flight sensor (10), for determining whether there is a signal coincidence of the at least two pixel signals (CLK1, CLK2) in a case where there is a signal coincidence, or to determine whether there is a signal coincidence of the at least two pixel signals (CLK1, CLK2) of the at least two pixels (SPAD1, SPAD2) of the photon counting time-of-flight sensor (10). Setting the counting operation mode to a coincidence counting operation mode in which counts of the at least two pixel signals are counted together; and generating a coincidence count signal (YES) for setting the count mode of operation to a coincidence count mode of operation. Preferably, the coincidence count signal corresponds to a temporally later pixel signal of the at least two pixel signals (CLK1, CLK2). For example, only one count will be recorded when no coincidence detection is detected. However, the count number of the common counter may be multiplied by two to reproduce the real number of events. Therefore, more counts can be accumulated, which can optimize the signal-to-noise ratio. Further, silicon area can be saved by taking into account correlations between adjacent / neighboring pixels in the sensor. This correlation is utilized to save the total counter bit length for two or more pixels in the group of pixels. Thus, this temporal correlation may be determined, and coincidence counts may be dynamically stored in a common (shared) counter.

Description

Technical Field

[0001] The present disclosure generally relates to photon counting circuitry and photon counting methods. Background Art

[0002] Generally, it is known to determine the distance based on the round-trip delay of the emitted light. For example, pulsed light or modulated light can be emitted and the time it takes to return to the image sensor can be measured. This technique can be called direct time of flight (dToF).

[0003] In dToF, photons can be "counted" by time-to-digital conversion and stored in a histogram. Photon detection can be achieved by detecting photoelectric avalanches (e.g., based on SPAD (single photon avalanche diode) technology, APD (avalanche photodiode), etc.). The photoelectric signal can indicate the number of photons or a single photon, and the number of photons can be stored in a corresponding counter, which may require a high enough bit length to store a sufficiently large number of photons.

[0004] Furthermore, photon counting techniques may be known, for example based on photodiodes, where a determined voltage or the like may indicate the number of photons.

[0005] While techniques exist for counting photons, it is generally desirable to provide a photon counting circuitry and a photon counting method. Summary of the invention

[0006] According to a first aspect, the present disclosure provides a photon counting circuit system configured to:

[0007] Determining whether there is a signal coincidence of at least two pixel signals based on a degree of temporal overlap of at least two pixel signals of at least two pixels of the photon counting time-of-flight sensor, for setting the counting operation mode to a coincidence counting operation mode if there is a signal coincidence, wherein counts of the at least two pixel signals are counted together in the coincidence counting operation mode; and

[0008] A coincidence count signal is generated for setting the counting operation mode to the coincidence count operation mode.

[0009] According to a second aspect, the present disclosure provides a photon counting method, comprising:

[0010] Determining whether there is a signal coincidence of at least two pixel signals based on a degree of temporal overlap of at least two pixel signals of at least two pixels of the photon counting time-of-flight sensor, for setting the counting operation mode to a coincidence counting operation mode if there is a signal coincidence, wherein counts of the at least two pixel signals are counted together in the coincidence counting operation mode; and

[0011] A coincidence count signal is generated for setting the counting operation mode to the coincidence count operation mode.

[0012] Further aspects are set out in the dependent claims, the following description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Embodiments are explained by way of example with reference to the accompanying drawings, in which:

[0014] Figure 1 A schematic diagram showing a SPAD-based photon counting pixel according to the present disclosure;

[0015] Figure 2 An embodiment of a photonic circuit system including a photon counting circuit system according to the present disclosure is shown in a block diagram;

[0016] Figure 3 shows a further embodiment of a photonic circuit system including a photon counting circuit system according to the present disclosure;

[0017] Figure 4 Show Figure 3 Timing diagram of the photon counting circuit system;

[0018] Figure 5 shows a photon counting ToF circuitry and a photon counting circuitry according to the present disclosure operating in a non-coincidence counting mode;

[0019] Figure 6 shows a photon counting ToF circuitry and a photon counting circuitry according to the present disclosure operating in a coincidence counting mode;

[0020] Figure 7 An embodiment of a photon counting method according to the present disclosure is shown, wherein it is determined whether there is a coincidence or a non-coincidence;

[0021] Figure 8 A further embodiment of the photon counting method according to the present disclosure is shown, wherein non-coincidence is determined;

[0022] Fig. 9 A further embodiment of the photon counting method according to the present disclosure is shown, wherein the presence of coincidence is determined;

[0023] Fig.10 A further embodiment of the photon counting method according to the present disclosure is shown, wherein the corresponding counters are set as common counters or individual counters, depending on whether there is a coincidence; and

[0024] Fig.11 A high-level diagram of a photon counting ToF camera including photon counting circuitry according to the present disclosure is shown. DETAILED DESCRIPTION

[0025] In from Figure 1 Before starting a detailed description of the embodiments, a general explanation is given.

[0026] As mentioned at the outset, methods for counting photons to determine distance or depth are generally known. However, as many counter bits as possible may be needed to increase the DR (dynamic range). It has been recognized that it may be desirable to increase the effective bit length of the counter and at the same time reduce the required silicon area, thereby providing a smaller pixel design pitch.

[0027] It is further recognized that there may be temporal (in the time domain) coherence / coincidence between pixels (adjacent / nearby, not limiting the present disclosure in this regard) of a photon counting ToF sensor, which can be used to reduce the counter length. It should be noted that the present disclosure is not limited to active light sensing known as ToF, but can also count photons from passive light (e.g., ambient light, sunlight, etc.) based on other sensor types.

[0028] Furthermore, it has been recognized that it may be desirable to provide a SPAD / APD based photon counting sensor that can be used in a binning mode. In state-of-the-art sensors, it has been recognized that binning is difficult to achieve without identifying simultaneously generated events. If no identification mechanism is implemented, in known sensors, all simultaneously generated events will be considered as one event. However, this may result in a decrease in the total effective counts and thereby reduce the SNR (signal-to-noise ratio), power efficiency, etc.

[0029] Therefore, some embodiments relate to a photon counting circuit system configured to: determine whether there is a signal coincidence of at least two pixel signals based on the degree of temporal overlap of at least two pixel signals of at least two pixels of a photon counting time-of-flight sensor, so as to set the counting operation mode to a coincidence counting operation mode when there is a signal coincidence, wherein, in the coincidence counting operation mode, the counts of at least two pixel signals are counted together; and generate a coincidence counting signal for setting the counting operation mode to the coincidence counting operation mode.

[0030] The circuit system may relate to any entity or entities that may be capable of use in the context of photon counting (time of flight) measurements, such as one or more processors (e.g., CPU (central processing unit), GPU (graphics processing unit)), one or more FPGA (field programmable gate array), etc. The circuit system may include or may be applicable to a camera (system), a computer (system), a server, etc.

[0031] Photon counting circuitry may be used to count photons based on a photoelectric signal, which may be generated by one or more SPADs (single photon avalanche diodes), APDs (avalanche photodiodes), or any other circuitry that may generate a signal indicative of one or more photons such that the number of incident photons may be inferred.

[0032] In general, the present disclosure is not limited to photon counting ToF technology, because 2D (two-dimensional) active or passive imaging can also apply the principles of the present disclosure. For example, the present disclosure can generally be applied based on photon counting, that is, any type of technology that can count photons other than ToF. Therefore, in some embodiments, the present disclosure can generally relate to photon counting circuit systems, photoelectric detection circuit systems, 2D imaging circuit systems, 3D imaging circuit systems, etc.

[0033] In addition, SPADs and the like may also be used in pixels of a photon counting time-of-flight sensor according to the present disclosure for photodetection or photocounting. If a photon is incident on a pixel, the pixel may generate a pixel signal that temporally overlaps with another pixel signal of another pixel of the photon counting ToF sensor. The sensor may be any type of sensor, such as a single-layer sensor, a stacked sensor, a BSI (back side illumination) sensor, a FSI (front side illumination sensor), and the like.

[0034] Overlap in time may refer to a situation where at least two pixel signals are generated at approximately the same time. If they are indicated at exactly the same time (and, in some embodiments, if they also end at the same time), their degree of overlap may be determined as 100 percent (or any other way of expressing that they are generated completely in parallel). The corresponding internal times used to determine the degree of overlap in time may differ between pixels and may be calibrated separately so that it may be determined globally that at least two pixel signals overlap to a certain extent.

[0035] The degree may be less than one hundred percent (or "perfectly") if they are not generated exactly simultaneously, ie when at least two pixel signals are offset in time relative to each other.

[0036] For example, they may not overlap at all or overlap to a certain extent (e.g., fifty percent). For example, assuming the pixel signals have the same length: if a first pixel signal is generated at a first time point, and a second pixel signal may be generated at a second time point located in the middle of the first time point, the overlap may be fifty percent.

[0037] If the degree of overlap in time is high enough (ie, above or equal to a predetermined threshold), it can be determined that the signals are in agreement, or in other words, there is a signal agreement of at least two pixel signals. Of course, whether more than two pixel signals have agreement can be determined in a similar or identical manner.

[0038] If there is a signal coincidence, a coincidence counting mode of operation may be applied according to the present disclosure. In the coincidence counting mode of operation, the counts indicated by each of the at least two pixel signals are counted together (e.g., counted as one). For example, in the presence of a coincidence, the corresponding counts may be counted as one in a common counter shared by the at least two pixels.

[0039] In addition to the coincidence counting operation mode, in the case where there is no signal coincidence between at least two pixel signals, the non-coincidence counting operation mode can be determined as the counting operation mode. In this case, the corresponding counts can be stored in separate counters for at least two pixels.

[0040] In order to indicate or set the counting operation mode to be a coincidence counting operation mode, a coincidence count signal may be generated. The coincidence count signal may correspond to one of the at least two pixel signals, which may be reused or forwarded to a corresponding circuit system to "activate" a common counter (or any other circuit system for storing counts, such as a histogram).

[0041] In order to indicate or set a non-compliant counting operation mode as a counting operation mode, it may not be necessary to generate a corresponding signal, since the non-compliant counting operation mode can be determined based on the absence of a signal, and the present disclosure is not limited in this regard, since for a compliant counting operation mode, a signal can be used to explicitly set the non-compliant counting operation mode.

[0042] In some implementations, a non-coincidence count mode of operation may be indicated by a corresponding signal, and a coincidence count mode of operation may be determined based on the absence of the signal.

[0043] According to the present disclosure, silicon area can be saved. In a photon counting sensor according to the prior art, a counter with a sufficiently high bit length may be required to store all generated events. However, implementing a small pixel pitch design may be challenging because the counter in the prior art may occupy too much silicon area.

[0044] However, in accordance with the present disclosure, it has been recognized that correlations between adjacent / neighboring pixels in a sensor may need to be considered.

[0045] This correlation is exploited to save the total counter bit length of two or more pixels in a pixel group (e.g., 1×2, 2×1, 2×2, etc.). Therefore, according to the present disclosure, such temporal correlation (i.e., coincidence) can be detected / determined, and the coincidence count can be stored in a common (shared) counter. By doing so, unlike counting each pixel by a separate counter, the coincidence count does not need to be stored multiple times in each of the separate counters, but only once in the common counter. Therefore, the total counter bit length of the pixel group can be reduced, and silicon area can be saved thereby.

[0046] In some embodiments, the photon counting circuitry is further configured to determine the counting operating mode as a non-coincidence counting operating mode if the degree of temporal overlap of at least two pixel signals is below a predetermined threshold, as discussed herein.

[0047] In some embodiments, the photon counting circuitry is further configured to, in a coincidence counting mode of operation, store photon counts indicated by the at least two pixel signals in a common counter that is common to the at least two pixels, as discussed herein.

[0048] In some embodiments, the photon counting circuitry is further configured to store a coincident photon count of at least two pixel signals as one count in a common counter in a coincidence counting mode of operation, as discussed herein.

[0049] In some embodiments, the photon counting circuitry is further configured to: in a non-coincidence counting mode of operation, store the photon count indicated by the at least two pixel signals in a separate counter for each of the at least two pixel signals, as discussed herein.

[0050] In some embodiments, the coincidence count signal is a clock signal. However, as discussed above, the coincidence count signal can be one of the at least two pixel signals, which can be reused, etc. (also as a clock signal). In addition, the clock signal can be generated in response to receiving one of the at least two pixel signals.

[0051] In some embodiments, the coincidence count signal corresponds to the later pixel signal in time of the at least two pixel signals. Therefore, before controlling the corresponding counter, it may be ensured that there is a coincidence first, because it may take a certain time to determine whether there is a coincidence.

[0052] In some embodiments, photon counting further includes at least three counters, including at least one common counter for a coincidence counting mode of operation, and at least two separate counters for a non-coincidence counting mode of operation, as discussed below (e.g., with reference to Figure 2 , Figure 5 or Figure 6 ).

[0053] In some embodiments, the photon counting circuit system further includes: four counters, including first to fourth counters, and the circuit system can be further configured to: based on the coincidence count signal, set the first counter and the second counter as common counters for the coincidence count operation mode, as will be discussed below (e.g., with reference to Figure 5 and Figure 6 ).

[0054] In some embodiments, the photon counting circuit system is further configured to: based on the absence of the coincidence count signal, set the first counter and the third counter to a first separate counter, and set the second counter and the fourth counter to a second separate counter, as will be discussed below (e.g., with reference to Figure 5 and Figure 6 ).

[0055] In general, by setting the above-mentioned corresponding counters, a dynamically adaptable counting circuit system can be provided, which can dynamically switch between common counting and individual counting depending on whether there is a coincidence. Thereby, the amount of storage can be optimized, for example, because the required storage can be reduced (if two counts are stored together as one) and the possible storage can be increased, because, for example, two (smaller) counters are used as one large counter that can store the coincidence count. If there is a non-coincidence, the common counter can be dynamically set to an individual counter, thereby optimizing the spatial resolution in the case of a non-coincidence.

[0056] Some embodiments relate to a photon counting method, comprising: determining whether there is a signal coincidence of at least two pixel signals based on the degree of temporal overlap of at least two pixel signals of at least two pixels of a photon counting time-of-flight sensor, so as to set a counting operation mode to a coincidence counting operation mode when there is a signal coincidence, wherein, in the coincidence counting operation mode, the counts of at least two pixel signals are counted together; and generating a coincidence counting signal for setting the counting operation mode to the coincidence counting operation mode, as discussed herein.

[0057] The methods described herein may be performed by photon counting circuitry according to the present disclosure.

[0058] In some embodiments, the photon counting method further includes: if the degree of temporal overlap of the at least two pixel signals is below a predetermined threshold, determining the counting operation mode as a non-coincidence counting operation mode, as discussed herein. In some embodiments, the photon counting method further includes: in the coincidence counting operation mode, storing the photon count indicated by the at least two pixel signals in a common counter that is common to the at least two pixels, as discussed herein. In some embodiments, the photon counting method further includes: in the coincidence counting operation mode, storing a coincidence photon count of the at least two pixel signals as a count in the common counter, as discussed herein. In some embodiments, the photon counting method further includes: in the non-coincidence counting operation mode, storing the photon count indicated by the at least two pixel signals in a separate counter for each of the at least two pixel signals, as discussed herein. In some embodiments, the coincidence count signal is a clock signal, as discussed herein. In some embodiments, the coincidence count signal corresponds to the later pixel signal in time of the at least two pixel signals, as discussed herein. In some embodiments, the photon counting method applies at least three counters, including at least one common counter for a coincidence counting mode of operation, and at least two separate counters for a non-coincidence counting mode of operation, as discussed herein. In some embodiments, the photon counting method applies four counters, including first to fourth counters, the method further comprising: based on a coincidence counting signal, setting the first counter and the second counter as a common counter for the coincidence counting mode of operation, as discussed herein. In some embodiments, the photon counting method further comprises: based on the absence of a coincidence counting signal, setting the first counter and the third counter as a first separate counter, and setting the second counter and the fourth counter as a second separate counter, as discussed herein.

[0059] The method as described herein is also implemented as a computer program in some embodiments, which, when executed on a computer and / or a processor, causes the computer and / or the processor to perform the method. In some embodiments, a non-transitory computer-readable recording medium is also provided, in which a computer program product is stored, which, when executed by a processor (such as the above-mentioned processor), causes the method described herein to be performed.

[0060] Return to Figure 1, shows a schematic diagram of a SPAD-based photon counting pixel 1 and a PFE (pixel front end element (circuitry)). In this embodiment, a SPAD 2 device biased in Geiger mode generates a pulse at its anode, i.e. a so-called "event" is generated. This pulse can be filtered by a comparator / inverter (or any other interface circuitry) and then the events are counted by a counter 3.

[0061] It should be noted that Figure 1 In the figure, two pixels are shown for illustration purposes, but in general, the present disclosure can also be applied to more pixels.

[0062] In this embodiment, for simplicity, SPAD 2 is depicted as a passive quenching structure, but it can be an actively quenched SPAD, an externally clocked quenched SPAD, etc. In addition, the present disclosure is not limited to SPADs, but can also be applied to any other pixel based on one or more APDs or similar features that generate digital events in response to incident photons. Counter 3 is simplified to a counter block, but can be a ripple counter, a LFSR counter, or any other circuit system capable of accumulating events generated by a SPAD.

[0063] Figure 2 An embodiment of a photon counting ToF circuitry 10 is shown in a block diagram including photon counting circuitry 11 embodied as a “coincidence detection” block 11 .

[0064] In this embodiment, two pixels (such as Figure 1 As already shown in (not limiting the present disclosure in this regard), each pixel is based on a SPAD (ie, SPAD1 and SPAD2). The coincidence detection block 11 is configured to monitor the outputs of the clocks CLK1 and CLK2 of SPAD1 and SPAD2, respectively.

[0065] If the clock signals generated by the two SPADs (corresponding to the pixel signals, as described above), i.e., CLK1 and CLK2, are coincidence signals or have sufficiently high overlap in the time domain, the coincidence detection block determines that they are coincidence events and outputs YES (which means that they are coincidence events; the present disclosure is not limited to outputting YES, as any other way of expressing coincidence can be envisioned) to turn on the switch SW2, thereby allowing the generated coincidence clock signal CLK to be passed through the switch SW2 to the common counter 12. In this process, the other switch SW1 is turned off (i.e., kept in an off state).

[0066] If the clock signals CLK1 and CLK2 are not coincidence signals, the coincidence detection block determines that they are non-coincidence events and outputs NO (which means that they are not coincidence events), thereby turning on the switch SW1, allowing the two clock signals to be transmitted through the switch SW1 to the separate counter 13 of SPAD1 and the separate counter 13' of SPAD2.

[0067] In some implementations, the coincidence circuit may need some time to complete the determination and cause the use of buffered clock signals CLK1D and CLK2D, which are buffered versions of CLK1 and CLK2, respectively, caused by delay cells.

[0068] Figure 3 and Figure 4 A further embodiment of a photon counting ToF circuit system 20 including a photon counting circuit system 21 according to the present disclosure is shown ( Figure 3 ) and a clock diagram 30 (in Figure 4 middle).

[0069] exist Figure 3 In an embodiment, the outputs of two SPADs (ie, CLK1 and CLK2) are monitored and an additional clock signal CLK3 is generated. In this embodiment, the photon counting circuit system 21 is configured to detect an overlap between the clock signals CLK1 and CLK2, and output CLK3 when an overlap between CLK1 and CLK2 is detected.

[0070] Figure 4 Schematic diagrams a) and b) of exemplify implementations of clock signals in the case of overlap, whereas schematic diagrams c) and d) of exemplify implementations of clock signals in the case of non-overlap.

[0071] As can be seen from schematic diagrams a) and b), the clock signal CLK3 corresponds to the later clock signal in time between the clock signals CLK1 and CLK2. However, CLK3 is output only when the overlap between CLK1 and CLK2 is sufficient.

[0072] If there is no overlap, as shown in schematic diagrams c) and d), where the two clock signals CLK1 and CLK2 are completely non-overlapping, no signal is generated for CLK3.

[0073] According to the present disclosure, photon counting circuitry (e.g., Figure 3 , but the present disclosure is not limited in this regard). For example, if Figure 3The two pixels should be combined, and when they generate a coincident pixel signal as described herein (i.e., signals CLK1 and CLK2 overlap in time to some extent), only one count will be recorded when there is no coincidence detection. However, when the Figure 3 When the same or similar circuit system is applied to such a binned pixel, the number of counts of the common counter can be multiplied by two to reproduce the real number of events. Thus, more counts can be accumulated, which can optimize the signal-to-noise ratio (which usually corresponds to the square root of the number of counts).

[0074] Another embodiment of a photon counting ToF circuit system 40 including photon counting circuit system is depicted in Figure 5 and Figure 6 , the two figures depict the same circuit system, but in different operating states. Figure 5 The state in which the "coincidence counting mode" itself is deactivated and counters 41 and 42 always act together as a single counter for SPAD 1 and counters 43 and 44 always act together as a single counter for SPAD 2 is depicted. Figure 5 The circuit system operates as a differential mode counter.

[0075] exist Figure 6 , a state in which the "coincidence counting mode" is activated is shown, which means that a coincidence can be detected normally. In this state, if a coincidence is determined, counters 41 and 43 together act as a common counter for SPAD1 and SPAD2, and if there is no coincidence, counters 42 and 44 are separate counters. Therefore, Figure 6 The circuit system operates as a common mode counter.

[0076] In addition to the counters 41 to 44, a photon counting circuitry 45 is shown. As already discussed above, delay lines 46 and 47 are used to generate a delayed clock signal when non-coincidence is determined. In addition, a multiplexer with a control signal "ModSel" (mode select) is added to select the photon counting circuitry 45 in normal mode (each pixel has a separate counter, such as Figure 5 ) and shared counter mode (as shown Figure 6 The photon counting ToF circuit system 40 can be switched between the two modes as shown. This can bring flexibility in the circuit switching between these two modes.

[0077] When ModSel is zero ( Figure 5 In this mode, there are two separate counters based on counters 41 and 42 of SPAD1 and counters 43 and 44 of SPAD2. In this mode, each of the separate counters has log2(2 M +2 N), where M is the bit length of counters 42 and 44, and N is the bit length of counters 41 and 43, wherein the present disclosure is not limited to any particular bit length, and the bit lengths of counters 42 and 44 and 41 and 43 may be different from each other.

[0078] When ModSel is 1 ( Figure 6 When a coincidence is detected, a signal is generated by the photon counting circuitry 45 in the form of a clock signal (not depicted), but similar to Figure 4 a) or Figure 4 As shown in b).

[0079] This clock pulse is counted by the common counter formed by counters 41 and 43, as explained above. The common counter formed has a bit length of twice N. When no coincidence is detected, the photon counting circuitry 45 generates no signal, and the corresponding pixel signal is counted by counters 42 and 44, respectively, operating as separate counters.

[0080] For example, if the counter bit length N is seven and the counter bit length M is five, then the common counter has fourteen bits and thus can store fourteen bits (ie, log2(2 14 +2 5 ) common value and five-bit differential value, and in the mode where the coincidence count is not activated at all ( Figure 5 ), the total bit length is twelve bits.

[0081] Figure 7 An embodiment of a photon counting method 50 according to the present disclosure is shown in a block diagram.

[0082] At 51 , a determination is made as to whether a match exists, as discussed herein.

[0083] At 52, if it is determined that a coincidence exists, a coincidence count signal is generated, as discussed herein.

[0084] Figure 8 An embodiment of a photon counting method 60 according to the present disclosure is shown in a block diagram.

[0085] At 61 , it is determined that a non-compliance exists, as discussed herein.

[0086] At 62 , the photon counts are stored in separate counters, as discussed herein.

[0087] Fig. 9 An embodiment of a photon counting method 70 according to the present disclosure is shown in a block diagram.

[0088] At 71 , it is determined that there is a match, as discussed herein.

[0089] At 72, a coincidence count signal is generated, as discussed herein.

[0090] At 73, the coincidence photon counts are stored in a common counter, as discussed herein.

[0091] Fig.10 An embodiment of a photon counting method 75 according to the present disclosure is shown in a block diagram.

[0092] At 76 , a determination is made as to whether compliance exists, as discussed herein.

[0093] At 77, the corresponding counters are set as common counters or individual counters, depending on whether there is a match, as discussed herein.

[0094] exist Fig.11 , an embodiment of a photon counting time-of-flight imaging system 80 is shown at a high level, which is embodied herein as a photon counting ToF camera and can be used for depth sensing or providing distance measurement, and has a photon counting circuit system 87, which is configured to perform the methods discussed herein and form control for the photon counting ToF device 80 (and which includes (not shown) corresponding processors, memories and storage devices (i.e., counters, as discussed herein).

[0095] The photon counting ToF imaging system 80 has a pulsed light source 81 and it comprises a light emitting element (laser diode based), wherein in this embodiment the light emitting element is a narrow band laser element.

[0096] Light source 81 emits pulsed light to scene 82 (region of interest or object), and the scene reflects the light. By repeatedly emitting light to scene 82, scene 82 can be scanned, as known to those skilled in the art. The reflected light is focused by optical stack 83 to light detector 84.

[0097] The photon counting time-of-flight light detection circuitry 87 also forms the control of the light source, so that it also includes corresponding control circuitry (not depicted).

[0098] The photodetector 84 has: an image sensor 85 implemented based on a plurality of SPADs (single photon avalanche diodes) formed in an array of pixels (imaging elements); and a microlens array 86 that focuses light reflected from the scene 82 onto the image sensor 85 (to each pixel of the image sensor 85).

[0099] The light emission time information is fed from the light source 81 to a photon counting circuit system 87 including a photon counting unit 88, which also receives corresponding time information from the image sensor 85 when light reflected from the scene 82 is detected. Typically, the photon counting time-of-flight system is also capable of performing time-of-flight measurements. Based on the emission time information received from the light source 81 and the arrival time information received from the image sensor 85, the photon counting unit 88 calculates the round-trip time of the light emitted from the light source 81 and reflected by the scene 82, and on this basis calculates the distance d (depth information) between the image sensor 85 and the scene 82 based on the determination of the light event, as discussed herein. In addition, as discussed herein, the photon counting unit 88 has information about the time points at which the common mode counting and the differential mode counting are activated, so that the counts can be assigned separately.

[0100] The depth information is fed from the photon counting unit 88 to a 3D image reconstruction unit 89 of the photon counting circuitry 87 , which reconstructs (generates) a 3D image of the scene 82 based on the depth information received from the time-of-flight measurement unit 88 .

[0101] It should be appreciated that the embodiments describe methods with exemplary ordering of method steps. However, the specific ordering of the method steps is given for illustrative purposes only and should not be interpreted as binding. Changes in the ordering of the method steps may be obvious to a skilled person.

[0102] Please note that the division of control 87 into units 88 to 89 is for illustration purposes only, and the present disclosure is not limited to any particular functional division among the particular units. For example, control 87 may be implemented by a correspondingly programmed processor, a field programmable gate array (FPGA), or the like.

[0103] The methods described herein may also be implemented as a computer program that, when executed on a computer and / or processor, causes the computer and / or processor to perform the method. In some embodiments, a non-transitory computer-readable recording medium is also provided, in which a computer program product is stored, which, when executed by a processor (such as the above-mentioned processor), causes the described method to be performed. If not otherwise stated, all units and entities described in this specification and claimed in the attached claims may be implemented as integrated circuit logic (e.g., on a chip), and if not otherwise stated, the functions provided by such units and entities may be implemented by software.

[0104] To the extent that the above disclosed embodiments are implemented at least in part using software controlled data processing apparatus, it will be appreciated that providing such software controlled computer programs and transmission, storage or other media providing such computer programs are contemplated as aspects of the present disclosure.

[0105] Note that the present technology can also be configured as described below.

[0106] (1) A photon counting circuit system, configured to:

[0107] Determining whether there is a signal coincidence of at least two pixel signals based on a degree of temporal overlap of at least two pixel signals of at least two pixels of the photon counting time-of-flight sensor, for setting the counting operation mode to a coincidence counting operation mode if there is a signal coincidence, wherein counts of the at least two pixel signals are counted together in the coincidence counting operation mode; and

[0108] A coincidence count signal is generated for setting the counting operation mode to the coincidence count operation mode.

[0109] (2) The photon counting circuit system according to (1), further configured as follows:

[0110] If the temporal overlap degree of at least two pixel signals is lower than a predetermined threshold, the counting operation mode is determined to be a non-coincidence counting operation mode.

[0111] (3) The photon counting circuit system according to (1) or (2), further configured to:

[0112] In a coincidence counting mode of operation, photon counts indicated by at least two pixel signals are stored in a common counter that is common to the at least two pixels.

[0113] (4) The photon counting circuit system according to (3), further configured as follows:

[0114] In the coincidence counting mode of operation, a coincidence photon count of at least two pixel signals is stored as one count in a common counter.

[0115] (5) The photon counting circuit system according to any one of (1) to (4), further configured as follows:

[0116] In the non-coincidence counting mode of operation, the photon counts indicated by the at least two pixel signals are stored in a separate counter for each of the at least two pixel signals.

[0117] (6) The photon counting circuit system according to any one of (1) to (5), wherein the coincidence count signal is a clock signal.

[0118] (7) The photon counting circuit system according to (6), wherein the coincidence count signal corresponds to a pixel signal that is later in time among the at least two pixel signals.

[0119] (8) The photon counting circuit system according to any one of (1) to (7), further comprising: at least three counters, including at least one common counter for a coincidence counting operation mode, and at least two separate counters for a non-coincidence counting operation mode.

[0120] (9) The photon counting circuit system according to any one of (1) to (8), further comprising: four counters, including first to fourth counters, the circuit system being further configured as follows:

[0121] Based on the coincidence count signal, the first counter and the second counter are set as a common counter for the coincidence count operation mode.

[0122] (10) The photon counting circuit system according to (9), further configured to:

[0123] Based on the absence of the coincidence count signal, the first counter and the third counter are set to first individual counters, and the second counter and the fourth counter are set to second individual counters.

[0124] (11) A photon counting method comprising:

[0125] Determining whether there is a signal coincidence of at least two pixel signals based on a degree of temporal overlap of at least two pixel signals of at least two pixels of the photon counting time-of-flight sensor, for setting the counting operation mode to a coincidence counting operation mode if there is a signal coincidence, wherein counts of the at least two pixel signals are counted together in the coincidence counting operation mode; and

[0126] A coincidence count signal is generated for setting the counting operation mode to the coincidence count operation mode.

[0127] (12) The photon counting method according to (11), further comprising:

[0128] If the temporal overlap degree of at least two pixel signals is lower than a predetermined threshold, the counting operation mode is determined to be a non-coincidence counting operation mode.

[0129] (13) The photon counting method according to (11) or (12), further comprising:

[0130] In a coincidence counting mode of operation, photon counts indicated by at least two pixel signals are stored in a common counter that is common to the at least two pixels.

[0131] (14) The photon counting method according to (13), further comprising:

[0132] In the coincidence counting mode of operation, a coincidence photon count of at least two pixel signals is stored as one count in a common counter.

[0133] (15) The photon counting method according to any one of (11) to (14), further comprising:

[0134] In the non-coincidence counting mode of operation, the photon counts indicated by the at least two pixel signals are stored in a separate counter for each of the at least two pixel signals.

[0135] (16) The photon counting method according to any one of (11) to (15), wherein the coincidence count signal is a clock signal.

[0136] (17) The photon counting method according to (16), wherein the coincidence count signal corresponds to a pixel signal that is later in time among the at least two pixel signals.

[0137] (18) The photon counting method according to any one of (11) to (17), applying at least three counters, including at least one common counter for a coincidence counting operation mode, and at least two individual counters for a non-coincidence counting operation mode.

[0138] (19) The photon counting method according to any one of (11) to (18), wherein four counters are used, including a first counter to a fourth counter, and the method further comprises:

[0139] Based on the coincidence count signal, the first counter and the second counter are set as a common counter for the coincidence count operation mode.

[0140] (20) The photon counting method according to (19), further comprising:

[0141] Based on the absence of the coincidence count signal, the first counter and the third counter are set to first individual counters, and the second counter and the fourth counter are set to second individual counters.

[0142] (21) A computer program comprising a program code, which, when executed on a computer, causes the computer to execute the method according to any one of (11) to (20).

[0143] (22) A non-transitory computer-readable recording medium having a computer program product stored therein, which, when executed by a processor, causes the method according to any one of (11) to (20) to be performed.

Claims

1. A photon counting circuit system, configured to: Based on the degree of temporal overlap of at least two pixel signals of at least two pixels of the photon counting time-of-flight sensor, it is determined whether there is a signal coincidence of the at least two pixel signals, so as to set the counting operation mode to a coincidence counting operation mode when there is a signal coincidence, wherein: In the coincidence counting operation mode, counts of the at least two pixel signals are counted together; as well as A coincidence count signal is generated for setting the counting operation mode to the coincidence count operation mode.

2. The photon counting circuit system of claim 1 , further configured to: If the temporal overlap degree of the at least two pixel signals is lower than a predetermined threshold, the counting operation mode is determined as a non-coincidence counting operation mode.

3. The photon counting circuit system of claim 1 , further configured to: In the coincidence counting mode of operation, photon counts indicated by the at least two pixel signals are stored in a common counter, the common counter being common to the at least two pixels.

4. The photon counting circuit system of claim 3, further configured to: In the coincidence counting operation mode, a coincidence photon count of the at least two pixel signals is stored as a count in the common counter.

5. The photon counting circuit system of claim 1 , further configured to: In a non-coincidence counting mode of operation, the photon counts indicated by the at least two pixel signals are stored in a separate counter for each of the at least two pixel signals.

6. The photon counting circuit system of claim 1, wherein: The coincidence count signal is a clock signal.

7. The photon counting circuit system of claim 6, wherein: The coincidence count signal corresponds to a later pixel signal in time among the at least two pixel signals.

8. The photon counting circuit system of claim 1 , further comprising: At least three counters include at least one common counter for the coincidence counting mode of operation and at least two individual counters for the non-coincidence counting mode of operation.

9. The photon counting circuit system of claim 1 , further comprising: Four counters, including first to fourth counters, the circuit system is further configured to: Based on the coincidence count signal, the first counter and the second counter are set as common counters for the coincidence count operation mode.

10. The photon counting circuit system of claim 9, further configured to: Based on the absence of the coincidence count signal, the first counter and the third counter are set as first individual counters, and the second counter and the fourth counter are set as second individual counters.

11. A photon counting method, comprising: Determining whether there is a signal coincidence of at least two pixel signals of at least two pixels of the photon counting time-of-flight sensor based on a temporal overlap degree of the at least two pixel signals, so as to set the counting operation mode to a coincidence counting operation mode in the presence of the signal coincidence, wherein in the coincidence counting operation mode, counts of the at least two pixel signals are counted together; and A coincidence count signal is generated for setting the counting operation mode to the coincidence count operation mode.

12. The photon counting method according to claim 11, further comprising: If the temporal overlap degree of the at least two pixel signals is lower than a predetermined threshold, the counting operation mode is determined as a non-coincidence counting operation mode.

13. The photon counting method according to claim 11, further comprising: In the coincidence counting mode of operation, photon counts indicated by the at least two pixel signals are stored in a common counter, the common counter being common to the at least two pixels.

14. The photon counting method according to claim 13, further comprising: In the coincidence counting operation mode, a coincidence photon count of the at least two pixel signals is stored as a count in the common counter.

15. The photon counting method according to claim 11, further comprising: In a non-coincidence counting mode of operation, the photon counts indicated by the at least two pixel signals are stored in a separate counter for each of the at least two pixel signals.

16. The photon counting method according to claim 11, wherein: The coincidence count signal is a clock signal.

17. The photon counting method according to claim 16, wherein: The coincidence count signal corresponds to a later pixel signal in time among the at least two pixel signals.

18. The photon counting method of claim 11, applying at least three counters, including at least one common counter for the coincidence counting mode of operation, and at least two separate counters for non-coincidence counting mode of operation.

19. The photon counting method according to claim 11, using four counters, including a first counter to a fourth counter, the method further comprising: Based on the coincidence count signal, the first counter and the second counter are set as common counters for the coincidence count operation mode.

20. The photon counting method according to claim 19, further comprising: Based on the absence of the coincidence count signal, the first counter and the third counter are set as first individual counters, and the second counter and the fourth counter are set as second individual counters.

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