Proximity detection device and method

Abstract

Embodiments of the present disclosure relate to proximity detection devices and methods. The present disclosure relates to proximity detection devices. The proximity detection device includes one or more photodetectors and a readout circuit, the readout circuit being configured to sample one or more output signals from the one or more photodetectors at regular intervals throughout a detection period. The proximity detection device includes a pulse transmission circuit, the pulse transmission circuit being configured to transmit a first optical pulse having a first pulse duration and a second optical pulse having a second pulse duration into a scene, the second pulse duration being at least fifty percent longer than the first pulse duration.

Description

Technical Field

[0001] The present disclosure relates generally to the field of electrical devices, and in particular to proximity detection devices and proximity detection methods. Background Art

[0002] A proximity detection device (also called a proximity sensor) is a device that can detect the presence and / or range of an object in its field of view. Such a device typically emits radiation (e.g., infrared light) and analyzes the return signal in order to assess the range of one or more targets.

[0003] One technology that has been proposed for implementing proximity detection devices is SPAD (Single Photon Avalanche Diode) technology. In particular, SPAD arrays can be used for a variety of applications, including for ranging, for Z or 3D gesture recognition, and for 3D imaging. A proximity detection device based on a SPAD array typically includes a light source for transmitting an optical pulse into an image scene. The light reflected back from any object in the image scene is detected by the SPAD array and used to determine the flight time of the optical pulse. The distance from the object to the device can then be derived based on the flight time.

[0004] The detection of the returning optical pulse by the SPAD array is based on the detection of events in the cells of the SPAD array. In particular, each cell will provide an output pulse when a photon is detected, and by monitoring the events, the arrival time of the returning pulse can be estimated.

[0005] One difficulty with such event-driven systems is that in very high ambient light and / or with very reflective and / or very close targets, a large number of events may be captured and processed in a short time frame, leading to congestion. In addition, it may be difficult to accurately determine the timing of the return pulses due to noise and crosstalk. Summary of the invention

[0006] According to one aspect, a proximity detection device is provided, which includes: one or more photodetectors configured to generate an event in response to one or more optical pulses received from a scene; a readout circuit configured to sample one or more output signals from the one or more photodetectors at regular intervals throughout a detection period; and a pulse transmission circuit configured to transmit a first optical pulse having a first pulse duration and a second optical pulse having a second pulse duration into the scene, the pulse transmission circuit being configured so that each of the first optical pulse and the second optical pulse occurs at least partially during the detection period and so that the second pulse duration is at least 50% longer than the first pulse duration.

[0007] According to one embodiment, the pulse transmission circuit is configured such that the second pulse duration is at least four times longer than the first pulse duration.

[0008] According to one embodiment, the pulse transmission circuit is configured such that the first pulse duration is between 100 ps and 1 ns, and the second pulse duration is between 1 ns and 4 ns.

[0009] According to one embodiment, the readout circuit is configured to sample the one or more output signals at time intervals of 500 ps or less throughout the detection period.

[0010] According to one embodiment, the readout circuit is configured to sample the one or more output signals during a detection period having a duration of at least twice the sum of the first pulse duration and the second pulse duration.

[0011] According to one embodiment, the readout circuit includes a histogram memory configured to store samples captured throughout the detection period and accumulate samples captured during sampling periods of a plurality of detection periods in corresponding bins.

[0012] According to one embodiment, each photodetector of the one or more photodetectors is a single photon avalanche diode.

[0013] According to an embodiment, the pulse transmission circuit is configured to generate the start of the second optical pulse with a first time delay after the start of the first optical pulse, the first time delay being equal to at most half the duration of the detection period.

[0014] According to one embodiment, the pulse transmission circuit is configured to generate the start of the first optical pulse with a second time delay after the start of the second optical pulse, the second time delay being at least equal to half the duration of the detection period.

[0015] According to another aspect, a method for proximity detection is provided, the method comprising: transmitting a first optical pulse having a first pulse duration and a second optical pulse having a second pulse duration into a scene in an arbitrary order; and sampling one or more output signals from one or more photodetectors at regular intervals throughout a detection period, wherein the one or more photodetectors generate events in response to the one or more optical pulses received from the scene, each of the first optical pulse and the second optical pulse occurring at least partially during the detection period, and wherein the second pulse duration is at least 50% longer than the first pulse duration.

[0016] According to one embodiment, the second pulse duration is at least four times longer than the first pulse duration.

[0017] According to one embodiment, the first pulse duration is between 100 ps and 1 ns, and wherein the second pulse duration is between 1 ns and 4 ns.

[0018] According to one embodiment, one or more output signals are sampled at time intervals of 500 ps or less throughout the detection period.

[0019] According to one embodiment, the one or more output signals are sampled during a detection period having a duration of at least twice the sum of the first pulse duration and the second pulse duration.

[0020] According to one embodiment, the method further comprises storing samples captured throughout the detection periods in a memory, and accumulating samples captured during sampling periods of the plurality of detection periods in corresponding bins of the memory. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above features and advantages, as well as other features and advantages, will be described in detail in the following description of specific embodiments given by way of illustration and not limitation, with reference to the accompanying drawings, in which:

[0022] Figure 1 schematically illustrates a proximity detection device according to an example embodiment;

[0023] Figure 2 is a diagram illustrating one example of the timing of optical pulses according to a standard method;

[0024] Figure 3 is a diagram showing a transmitted optical pulse and a corresponding pulse generated by crosstalk;

[0025] Figure 4 is a diagram showing a captured signal in the presence of crosstalk;

[0026] Figure 5 is a diagram showing a returning optical pulse having a relatively low signal-to-noise ratio (SNR);

[0027] Figure 6 is a diagram illustrating the timing of optical pulses according to an example embodiment of the present disclosure;

[0028] Figure 7 schematically illustrates a SPAD array according to an example embodiment of the present disclosure;

[0029] Figure 8 Schematically illustrates a method for Figure 7 A readout circuit for a SPAD array; and

[0030] Fig. 9is a flow chart illustrating an example of operations in a proximity detection method according to an example embodiment. DETAILED DESCRIPTION

[0031] In the various drawings, the same features have been denoted by the same reference numerals. In particular, common structural and / or functional features between the various embodiments may have the same reference numerals, and may be provided with the same structures, dimensions, and material properties.

[0032] For the sake of clarity, only the operations and elements useful for understanding the embodiments described herein are described in detail. In particular, although embodiments of proximity detection devices in the form of SPAD arrays are described in this specification, the principles of the circuits and methods for proximity detection described herein can be applied to arrays formed by other types of photodetectors that generate events based on received optical stimuli.

[0033] Unless otherwise specified, when two elements are referred to as being connected together, it means a direct connection without any intermediate elements except conductors; and when two elements are referred to as being linked or coupled together, it means the two elements may be connected or they may be linked or coupled via one or more other elements.

[0034] Unless otherwise indicated, the expressions "about," "approximately," "substantially," and "in the order of" mean within 10%, preferably within 5%.

[0035] Figure 1 A proximity detection device 100 implementing a ranging function according to an example embodiment is schematically illustrated. In particular, the device 100 can generate, for example, a single range estimate for an object in an image scene, or can generate range estimates for various objects, for example in the form of a 3D depth map.

[0036] The apparatus 100 includes a light source 102, such as a laser, for generating an optical signal formed by a beam of optical pulses transmitted into an image scene, such as via a lens 104. In some embodiments, the light source 102 is a vertical cavity surface emitting laser (VCSEL). The return optical pulses are received, such as via another lens 106.

[0037] The device 100 also includes a range estimation circuit 108 for estimating the distance between the device 100 and one or more objects in the image scene reflected by the optical pulse. The range estimation circuit 108 includes, for example, a target SPAD array (TARGET SPAD) 110, which receives the return optical pulse via the lens 106. The target SPAD array 110 includes, for example, an array of one hundred to several hundred SPADs. Each SPAD generates an event after receiving one or more photons.

[0038] Range estimation circuit 108 also includes, for example, a reference SPAD array (REF SPAD) 112, which is, for example, of the same size or smaller than target SPAD array 110 and receives internal reflections of the transmitted optical pulses. In some embodiments, the reference SPAD array is a one-dimensional array (e.g., having only rows or columns of SPAD cells).

[0039] The delay detection circuit (DELAY DETECTION) 114 is coupled to the target SPAD array 110 and the reference SPAD array 112, for example, and estimates the delay between each emitted optical pulse and one or more return optical pulses received by the target SPAD array 110 to provide a range estimate (RANGE ESTIMATION) of the object. The delay detection circuit 114 includes, for example, a readout circuit (READOUT) 115, which is used to store the number of events captured by the target SPAD array 110 in the form of a histogram. The delay detection circuit 114 may further include a similar readout circuit 115', which is used to store the number of events captured by the reference SPAD array 112. The reference SPAD array 112 and the readout circuit 115' allow a differential readout to be obtained by determining the difference between the readout values. However, in some embodiments, the reference SPAD array 112 and the readout circuit 115' may be omitted, for example, depending on the desired accuracy and what calibration can be performed in the system.

[0040] The range estimation circuit 108 further includes, for example, a pulse generation circuit (PULSE GENERATION) 116 that generates a voltage signal VCSEL based on the timing signal CLK. The voltage signal VCSEL is provided to a laser modulation circuit (LASER MOD) 118 to generate a voltage or current signal for driving the light source 102. The advantage of using current rather than voltage to drive the light source 102 is that the power-current relationship is generally easier to control.

[0041] Figure 2is a graph illustrating an example of a signal VCSEL and represents the timing of optical pulses according to a standard method. In particular, the x-axis corresponds to time in nanoseconds (ns) and the y-axis represents the amplitude of the signal VCSEL. The optical pulses are transmitted at intervals corresponding to the detection period (DET PERIOD). Figure 2 An example of two consecutive pulses P transmitted at the beginning of a continuous detection period is illustrated. Figure 2 The dashed rectangle 202 in represents the return pulse from the scene, which is generally attenuated and spread out in time relative to the original transmitted pulse.

[0042] The inventors have noted that, as will now be referred to Figures 3 to 5 As described in more detail, there is a tradeoff in selecting the duration of each pulse of the optical signal in view of crosstalk and signal attenuation.

[0043] Figure 3 is a diagram illustrating an example of an optical pulse Pct generated by crosstalk and an optical pulse Pr corresponding to a signal received from a scene, the optical pulse Pct being composed of Figure 3 The cross-hatched curve in the figure indicates that the optical pulse Pr is Figure 3 The dashed line in is denoted. Curve c represents the decay over time as a function of the distance the pulse has travelled. Crosstalk in a proximity detection device corresponds to the portion of the transmitted optical pulse that is reflected directly back to the target SPAD array without passing through the scene.

[0044] exist Figure 3 In the example of , the optical pulse is relatively long, and therefore the pulse Pct caused by the crosstalk is also relatively long. In order to generate an estimate of the flight time of the optical pulse, the time Tmp of the midpoint of the pulse Pr is usually estimated. However, as will now be referred to Figure 4 As described, the overlap between the return optical pulses Pr and the crosstalk pulses Pct may lead to inaccurate range determination.

[0045] Figure 4 Is based on Figure 3 402. An example of a received optical pulse, a graphical representation of the return count (RETURN COUNT) (i.e., number of events) captured by a proximity detection device in the presence of crosstalk. It can be seen that the overlap between the crosstalk pulse Pct from the image scene and the optical pulse Pr results in a captured pulse 402 having an asymmetric shape. Extracting an accurate estimate of the timing of the midpoint Tmp of the received optical pulse Pr from such a deformed pulse is very difficult, not least because it does not have a uniform amplitude.

[0046] Figure 5is a diagram representing an example of a signal captured by a proximity detection device during a detection period DET PERIOD. In the case of relatively short optical pulses, the energy contained in such pulses will be relatively low. This may result in a weak return pulse Pr', in particular a signal with a relatively low signal-to-noise ratio (SNR).

[0047] Thus, the inventors have found that in known proximity detection devices there is typically a compromise between transmitting relatively short optical pulses and reducing the risk of inaccuracies due to crosstalk, and transmitting relatively long optical pulses and ensuring a relatively high SNR.

[0048] Figure 6 is a diagram illustrating the timing of optical pulses according to an example embodiment of the present disclosure, and in particular illustrates the form of a signal VCSEL used to generate the optical pulses.

[0049] According to embodiments described herein, optical pulses having at least two different durations are transmitted by the proximity detection device to the scene. For example, the pulse generation circuit 116 is configured to generate Figure 6 The signal VCSEL shown causes the optical signal to have an optical pulse of a similar form.

[0050] like Figure 6 As shown, each pulse during the same detection period (DET PERIOD) occurs at least partially during the detection period. As described above, the detection period corresponds to the following period: during this period, the output signal from the photodetector of the proximity detection device is sampled at regular intervals to generate a histogram that can be used for range estimation. In one embodiment, the readout circuit 115 is configured to sample one or more output signals at time intervals of 500 picoseconds (ps) or less throughout the detection period.

[0051] exist Figure 6 In the example of , pulse P1 appears at the beginning of each detection period and has a relatively short pulse duration Ds. The second pulse P2 appears at about half of the detection period and has a relatively long pulse duration D1. For example, pulse duration D1 is at least 50% longer than pulse duration Ds, and in some embodiments is at least four times longer than pulse duration Ds. In addition, in some embodiments, pulse duration Ds is between 100ps and 1ns, and pulse duration D1 is between 1ns and 4ns.

[0052] In some embodiments, the duration of the detection period is at least twice the sum of the pulse durations Ds and D1. In some embodiments, the duration of the detection period is between 10ns and 50ns, but other values ​​are also possible, for example, depending on the duration of the long pulse and the short pulse.

[0053] In each detection period, the delay between the start of pulse P1 and the start of pulse P2 (in Figure 6 The delay is at most 50% of the duration of the detection period, for example, when pulse P1 is shorter than pulse P2. In some embodiments, the delay is equal to less than 50% of the duration of the detection period (e.g., equal to 40% or less of the duration of the detection period), thereby providing a longer duration and thus providing a greater distance detection capability using relatively longer pulses.

[0054] In an alternative embodiment, the order of pulses P1 and P2 in each detection period can be reversed, with pulse P2 occurring at the beginning of each detection period. In this case, in each detection period, the delay between the beginning of pulse P2 and the beginning of pulse P1 is, for example, equal to at least 50% of the duration of the detection period. In some embodiments, the delay is equal to more than 50% of the duration of the detection period (e.g., at least 60% of the duration of the detection period), thereby providing a longer duration and therefore greater distance detection using relatively longer pulses.

[0055] It is obvious to those skilled in the art that although Figure 6 The first pulse ( Figure 6 The start of the pulse P1 in each detection period coincides with the start of the detection period, but in alternative embodiments, the timing may be different. For example, depending on the range expected to be captured by the proximity detection device, the first pulse may start after the start of the detection period, or the detection period may start after the start of the first pulse.

[0056] Figure 6 Also illustrated are dashed rectangles Prs and Prl, which represent examples of the form of return pulses from the scene in response to pulses P1 and P2, respectively. Pulse P1, for example, allows the midpoint of the return pulse Prs to be detected in the time range Rs represented by the shaded area in the return pulse Prs. In some embodiments, the time range Rs corresponds to a flight time between 0ns and 2.5ns, corresponding to a capture object range between 0cm and 37.5cm. Similarly, pulse P2, for example, allows the midpoint of the return pulse to be detected in the time range R1 represented by the shaded area in the return pulse Prl. In some embodiments, the time range R1 corresponds to a flight time between 2.5ns and 9ns, corresponding to a capture object range between 37.5cm and 135cm. Of course, the distance range aimed at by pulses P1 and P2 will depend on the specific use of the proximity detection device.

[0057] Figure 7A more detailed diagram according to an example embodiment is schematically illustrated. Figure 1 The target SPAD array 110. The SPAD array 110 is formed, for example, by an array of cells 702, each cell comprising a sub-array 704 of SPADs and an OR tree 706 for capturing events generated by the sub-array 704. Figure 7 In the example of , each subarray 704 corresponds to an arrangement of nine SPADs in three by three blocks, but different numbers and arrangements of SPADs are possible. The output lines of the "OR" tree of cells 702 together form, for example, n output lines 708 of the SPAD array 110, where n is equal to the number of cells 702. In one example, n is equal to a number between 1 and several hundred.

[0058] Figure 8 The following schematically illustrates in more detail a method according to an exemplary embodiment of the present invention. Figure 1 The readout circuit 115 'is implemented, for example, by a similar circuit coupled to the output of the reference SPAD array 112. The n output lines 708 from the SPAD array 110 are, for example, respectively coupled to the n sampling circuits SC_1 to SC_n of the sampling block 802. Each of these sampling circuits receives, for example, a series of p clock signals CLK1 to CLKp generated by a phase-locked loop (PLL) 804. Each of these clock signals has, for example, a frequency of approximately 1 GHz. The p clock signals CLK1 to CLKp are, for example, phase-shifted relative to each other so that they have significant edges at intervals throughout a sub-period of the detection period. For example, the sampling period SP is called, and the duration of the sub-period is pxSP ps. In some embodiments, the sampling period SP is equal to 125 ps, in other words, each sampling circuit SC_1 to SC_n generates samples at intervals of 125 ps. More generally, the sampling period SP may be between 50 ps and 500 ps, ​​and the clock signals CLK1 to CLKp may each have a frequency in the range of 100 kHz to 5 GHz.

[0059] Each of the sampling circuits SC_1 to SC_n generates, for example, an m-bit output signal, where m is, for example, equal to between 4 and 16, and is, for example, equal to 8. These signals are provided to an adder (ADDER) 806, which is, for example, timed by a clock signal CLK1 from a PLL 804 and, at each sampling instant, for example, adds the m-bit signals from all of the sampling circuits SC_1 to SC_n bit by bit to generate p output signals (p OP SIGNALS), where Figure 8 In the example of Figure 8In the example of , each of the p values ​​is a 5-bit value, but different bit lengths are possible. These values ​​provide p continuous samples stored in the histogram memory (HISTOGRAM MEMORY) 808. The detection period is formed by, for example, a set of q continuous p samples. For example, in one embodiment, each set of p samples corresponds to 8 samples spaced at 125ps, corresponding to a duration of 1ns. The detection period corresponds to, for example, 18 continuous groups of p samples, and therefore the duration is equal to 18ns. Of course, other values ​​of p and q are possible.

[0060] The scheduler (DISPATCHER) 810 provides a control signal CTRL to the histogram memory 808, for example, to control the storage of samples in q blocks of the memory, so that the memory can output pxq samples corresponding to the entire detection period on the output bus 812. In one example, the output bus provides 144 bins (i.e., p=8 and q=18), each with 21 bits. For example, the detection sequence of each detection period is repeated thousands of times, and the corresponding events are accumulated in the histogram memory 808. Assuming that during each detection period, each bin receives a maximum count of 16, a 21-bit output signal can be achieved by accumulating counts within 65536 detection periods.

[0061] It will be apparent to those skilled in the art that the samples representing the detection period stored in the histogram memory 808 may be processed to accurately determine the timing of one or more return pulses and thereby detect one or more target ranges in the scene.

[0062] Fig. 9 is a flow chart illustrating an example of operations in a proximity detection method according to an example embodiment. These operations are, for example, Figure 1 The circuit elements 116 , 118 , 102 , and 115 of the proximity detection device 100 are implemented.

[0063] In operation 901 , a first optical pulse having a first pulse duration is transmitted by circuit elements 116 , 118 , and 102 into a scene.

[0064] In operation 902, a second optical pulse having a second pulse duration is transmitted into the scene by circuit elements 116, 118, and 102. As described above, the second pulse duration is, for example, at least 50% longer than the first pulse duration. The order of operations 901 and 902 may be reversed.

[0065] In operation 903, one or more ranges are determined based on histogram data generated by: using readout circuit 115, sampling one or more output signals from one or more photodetectors of the proximity detection device at regular intervals throughout a detection period (and in some embodiments, for multiple detection periods). The detection period includes at least a portion of the transmission period of the first optical pulse and at least a portion of the transmission period of the second optical pulse. In practice, each detection period is continuous, and at least the second optical pulse will occur entirely during the detection period.

[0066] An advantage of the embodiments described herein is that by using optical pulses of different pulse durations during each detection period, objects at relatively short and relatively long ranges can be detected with good accuracy. In particular, relatively short optical pulses allow detection of objects at relatively short distances with relatively little crosstalk interference, while relatively long optical pulses allow detection of objects at relatively long distances while maintaining a good signal-to-noise ratio.

[0067] Various embodiments and variations have been described. Those skilled in the art will appreciate that certain features of these embodiments may be combined, and that other variations will readily occur to those skilled in the art. In particular, although reference has been made to Figure 7 and Figure 8 Examples of SPAD arrays and readout circuits are described, but these circuits represent only one example implementation and many variations are possible. For example, in some embodiments, the output signal from each cell in the SPAD array 702 may be processed individually (rather than using Figure 8 The samples are combined by an adder 806) to generate a 3D depth map.

[0068] Furthermore, although an example has been described in which two optical pulses are transmitted during each detection period, in alternative embodiments, three or more optical pulses of different pulse durations may be transmitted during each detection period.

[0069] Furthermore, rather than being implemented by SPAD devices, the photodetectors described herein may be implemented by APDs (avalanche photodiodes), and the photodetector array may be implemented by SiPMs (silicon photon multipliers) corresponding to an array of APDs. For example, SiPMs may be coupled with relatively fast analog readout circuits and ADCs to produce a histogram similar to that obtained by a SPAD array. One advantage of using a SPAD array is that this allows the use of fully digital implementation techniques.

[0070] The various embodiments described above can be combined to provide other embodiments. These and other changes can be made to the embodiments according to the above detailed description. Generally, in the appended claims, the terms used should not be interpreted as limiting the claims to the specific embodiments disclosed in the specification and claims, but should be interpreted as including all possible embodiments and the full range of equivalents given by such claims. Therefore, the claims are not limited by the present disclosure.

Claims

1. A proximity detection device, comprising: One or more photodetectors configured to: receiving one or more optical pulses reflected from a scene; as well as outputting one or more output signals based on the one or more optical pulses; a readout circuit configured to sample the one or more output signals at regular intervals throughout a detection period; as well as The pulse transmission circuit is configured as follows: transmitting a first optical pulse having a first pulse duration into the scene; as well as A second optical pulse having a second pulse duration is transmitted into the scene, wherein the second pulse duration is at least 50% longer than the first pulse duration, wherein the pulse transmission circuit is configured to at least partially transmit the first optical pulse and the second optical pulse during the detection period. 2 . The proximity detection device of claim 1 , wherein the pulse transmission circuit is configured to transmit the second optical pulse having the second pulse duration at least four times longer than the first pulse duration. 3 . The proximity detection device of claim 2 , wherein the first pulse duration is between 100 picoseconds (ps) and 1 nanosecond (ns), and the second pulse duration is between 1 ns and 4 ns. 4 . The proximity detection device of claim 1 , wherein the readout circuit is configured to sample the one or more output signals at time intervals of 500 ps or less throughout the detection period.

5. The proximity detection device of claim 1 , wherein the readout circuit is configured to sample the one or more output signals during the detection period, the duration of the detection period being at least twice the sum of the first pulse duration and the second pulse duration.

6. A proximity detection device according to claim 1, wherein the readout circuit includes a memory, which is configured to store samples of the one or more output signals captured throughout the detection period and accumulate corresponding samples captured during corresponding sampling periods of multiple detection periods in corresponding bins. 7 . The proximity detection device of claim 1 , wherein each of the one or more photodetectors is a single photon avalanche diode.

8. The proximity detection device of claim 1, wherein the pulse transmission circuit is configured to start transmitting the second optical pulse a first time delay after starting transmitting the first optical pulse, wherein the first time delay is at most half of the detection period.

9. The proximity detection device of claim 1, wherein the pulse transmission circuit is configured to start transmitting the first optical pulse at a second time delay after starting transmitting the second optical pulse, wherein the second time delay is at least half of the detection period.

10. A method for proximity detection, comprising: transmitting into the scene a first optical pulse having a first pulse duration and a second optical pulse having a second pulse duration, the second pulse duration being at least 50% longer than the first pulse duration; receiving, by one or more photodetectors, an optical signal reflected by the scene, and outputting, by the one or more photodetectors, one or more output signals based on the optical signal; as well as The one or more output signals are sampled at regular intervals throughout a detection period, wherein each of the first optical pulse and the second optical pulse is at least partially transmitted during the detection period. The method of claim 10 , wherein the second pulse duration is at least four times longer than the first pulse duration.

12. The method of claim 11, wherein the first pulse duration is between 100 picoseconds (ps) and 1 nanosecond (ns), and wherein the second pulse duration is between 1 ns and 4 ns.

13. The method of claim 10, wherein the one or more output signals are sampled at time intervals of 500 ps or less throughout the detection period.

14. The method of claim 10, wherein the duration of the detection period is at least twice the sum of the first pulse duration and the second pulse duration.

15. The method according to claim 10, further comprising: Samples of the one or more output signals captured throughout the detection period are stored in a memory, and corresponding samples captured during corresponding sampling periods of a plurality of detection periods are accumulated in corresponding bins of the memory.

16. The method of claim 10, wherein each of the one or more photodetectors is a single photon avalanche diode.

17. A proximity detection device, comprising: Single Photon Avalanche Diode (SPAD) arrays, configured as: receiving one or more optical pulses reflected from a scene; as well as outputting one or more output signals based on the one or more optical pulses; a readout circuit configured to sample the one or more output signals at regular intervals throughout a detection period; The pulse transmission circuit is configured as follows: transmitting a first optical pulse having a first pulse duration into the scene; as well as transmitting a second optical pulse having a second pulse duration into the scene, the second pulse duration being at least 50% longer than the first pulse duration, wherein the pulse transmission circuit is configured to transmit the first optical pulse and the second optical pulse at least partially during the detection period; as well as The pulse generator is configured to generate a signal based on the clock signal and output the signal to drive the pulse transmission circuit.

18. The proximity detection device of claim 17, wherein the pulse transmission circuit is configured to transmit the second optical pulse having the second pulse duration at least four times longer than the first pulse duration.

19. The proximity detection device of claim 18, wherein the first pulse duration is between 100 picoseconds (ps) and 1 nanosecond (ns), and the second pulse duration is between 1 ns and 4 ns.

20. The proximity detection device of claim 17, wherein the readout circuit is configured to sample the one or more output signals at time intervals of 500 ps or less throughout the detection period.

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