LIDAR system including a Geiger-mode avalanche photodiode based receiver with pixels having multiple return capabilities

Abstract

Disclosed are Geiger-mode avalanche photodiode-based LiDAR systems and methods that utilize a periodic series of light pulses to interrogate a detection area, detecting reflections of the periodic series of light pulses via a receiver comprising a plurality of Geiger-mode avalanche photodiode-based pixels. The pixels of the receiver are configured to asynchronously deactivate and reactivate after absorption of the reflections. As a result, each pixel can detect multiple reflections of the same light pulse during a single detection frame whose duration is defined by the periodicity of the series of light pulses. In addition, each pixel can store time-of-flight data for each of the multiple reflections detected during the detection frame. Therefore, once each individual pixel of the receiver detects a first reflection, each individual pixel of the receiver is not unaware and inoperable for the remainder of the detection frame.

Description

Technical Field

[0001] The present disclosure relates generally to scanning optical ranging and detection systems and methods, and more particularly to time-of-flight light detection and ranging (LiDAR) systems and methods employing Geiger-mode avalanche photodiodes. Background Art

[0002] Light detection and ranging (LiDAR) systems enable the measurement of the distance of one or more objects within an environment without physically contacting those objects. Time-of-flight (TOF) LiDAR estimates the range from a source to an object by sending a light pulse (typically a laser pulse) toward the object at a first time, detecting the reflection of the light pulse by the object at a second time, and determining the difference between the first time and the second time, the difference representing the time required for the light to travel to and from the object (i.e., the flight time of the light pulse). TOF LiDAR systems are attractive for use in many applications such as self-driving cars, agricultural equipment, etc. Summary of the invention

[0003] According to aspects of the present disclosure directed to Geiger-mode avalanche photodiode-based LiDAR systems and methods that enable each pixel of a multi-pixel detector to detect multiple reflections during each detection frame of an image frame, advances in the art have been made.

[0004] As with prior art systems and methods, embodiments according to the present disclosure interrogate a detection region using a pulsed laser and a receiver, the receiver comprising an array of pixels in which each pixel comprises a Geiger-mode avalanche photodiode. The pulsed laser directs a periodic series of light pulses into the detection region, and the receiver detects reflections of the light pulses from an object within the detection region during each of a series of detection frames, wherein the start of each detection frame is based on the emission of a different light pulse. When at least some of the light pulses are reflected back from an object within the detection region to a pixel of the detector, an avalanche detection event is triggered at the avalanche photodiode of the pixel, and the range to the object is estimated based on the time between the emission of the light pulse and the time when the avalanche detection event occurs (i.e., the flight time of one or more photons contained in the reflection). Unfortunately, in prior art TOF LiDAR systems, once an avalanche detection event is triggered during a detection frame, the pixel is rendered unavailable until it is reset at the start of the next detection frame. As a result, each pixel of the detector can only detect one reflection in each detection frame, and is unaware of the remainder of any detection frame in which a reflection has been detected.

[0005] In sharp contrast to the prior art, a LiDAR system according to the present disclosure includes a receiver whose pixels include circuitry that enables each pixel to detect more than one reflection during a single detection frame (referred to as "multiple-return capability"). As a result, after a pixel detects one reflection, the pixel is not unaware for the remainder of the detection frame. Circuitry included in each pixel enables its Geiger-mode avalanche photodiode to be asynchronously and automatically reset after each avalanche detection event so it can be quickly deactivated to stop the avalanche event and then reactivated to enable it to detect another reflection. Each pixel also includes multiple registers for maintaining timestamps associated with each avalanche detection event that occurs within a single detection frame, wherein each timestamp indicates a round-trip flight time of a light pulse between the LiDAR system and the object from which the reflection was received.

[0006] An exemplary embodiment according to the present disclosure is a TOF LiDAR system, which includes: a source, the source is used to emit a periodic series of light pulses toward a detection field; a receiver, the receiver is used to detect reflections from the detection area; and a processor, the processor is used to provide selection signals and control signals to the source and the receiver, and estimate the range of one or more objects in the detection area based on TOF data received from the receiver.

[0007] The receiver includes: a pixel array in which each pixel includes a Geiger-mode avalanche photodiode for detecting reflections from a detection area; a strobe signal controller for automatically deactivating the GmAPD after an avalanche detection event in response to absorption of the reflections and reactivating the GmAPD to enable detection of subsequent reflections; a TOF counter for tracking the time between emission of a light pulse and detection of a reflection of the light pulse; and a TOF register module for storing TOF data associated with multiple reflections detected by the GmAPD during a single detection frame.

[0008] In some embodiments, the gating signal controller includes a holdoff timer and an activation timer. The holdoff timer initiates automatic, asynchronous deactivation and quenching of the GmAPD upon detection of an avalanche detection event. The activation timer initiates asynchronous reactivation of the GmAPD in response to a signal from the holdoff timer, or initiates synchronous activation of the GmAPD in response to a global activation signal from a processor.

[0009] In some embodiments, the TOF register module includes two register groups and a controller. One register group includes multiple TOF registers for storing time-of-flight information of reflections detected during an activated detection frame, and the second group includes TOF registers for reading out time-of-flight information of reflections detected during a previous detection frame.

[0010] An embodiment according to the present disclosure includes a light detection and ranging (LiDAR) system, the light detection and ranging (LiDAR) system comprising: a light source, the light source is used to emit a series of light pulses toward a detection area, wherein the light pulses in the series of light pulses are periodic and separated by a period T1; and a receiver, the receiver comprising a plurality of pixels, the plurality of pixels being used to detect reflections of the light pulses during each detection frame in a plurality of detection frames, each detection frame having a duration based on T1 and having a start time based on the emission of different light pulses in the series of light pulses, wherein each pixel comprises: (i) a Geiger mode avalanche photodiode (GmAPD), the GmAPD being used to detect reflections of the light pulses from the detection area; (ii) ) a gating signal controller for activating the GmAPD to place it in Geiger mode and deactivating the GmAPD to take it out of Geiger mode; (iii) a counter for tracking the time of flight (TOF) between the emission of a light pulse in a series of light pulses and the detection of one or more reflections of the light pulse in the series of light pulses; (iv) a TOF register module for storing TOF data associated with one or more reflections of the light pulse in the series of light pulses; wherein the LiDAR system is characterized in that each pixel of the receiver is configured so that it is operable to detect multiple reflections of each light pulse in the series of light pulses during each detection frame in a plurality of detection frames.

[0011] According to another embodiment of the present disclosure, a method for estimating the range of at least one object in a detection area includes: emitting a series of light pulses toward the detection area, wherein the light pulses in the series of light pulses are periodic and separated by a period T1; defining a plurality of detection frames having a duration T1, wherein each detection frame has a start time based on the emission of different light pulses in the series of light pulses; receiving a first reflection of a first light pulse in the series of light pulses at a first pixel of a receiver during a first detection frame in the plurality of detection frames, wherein the first pixel includes a first Geiger-mode avalanche photodiode (GmAPD), and wherein receiving the first reflection triggers a first avalanche detection event; asynchronously deactivating the first GmAPD to quench the first avalanche detection event; and asynchronously activating the first GmAPD to initiate a second avalanche detection event in response to receiving a second reflection of the first light pulse in the series of light pulses during the first detection frame. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] 1A-1B depict schematic diagrams of a TOF LiDAR system according to the prior art.

[0013] 2 depicts an illustrative timing diagram of multiple waveforms including a representative image frame of one pixel of a receiver of a TOF LiDAR system, such as the TOF LiDAR system previously shown and described in FIGS. 1A-1B .

[0014] Figure 3 A schematic diagram of an illustrative embodiment of a LiDAR system according to the present disclosure is depicted.

[0015] Figure 4 Depicted is a schematic diagram of a detector in accordance with an illustrative embodiment.

[0016] Figure 5 Depicted is a functional block diagram of a detector pixel in accordance with an illustrative embodiment.

[0017] Figure 6 Operation of a method for interrogating a detection zone in accordance with the present disclosure is depicted.

[0018] Figure 7 Depicted are sub-operations of an exemplary sub-method suitable for enabling a pixel to detect multiple reflections during a single detection frame in accordance with the present disclosure.

[0019] Figure 8 A timing diagram of a representative detection frame for one pixel 404 according to sub-method 700 is depicted.

[0020] Fig. 9 An exemplary circuit arrangement of a gating-signal controller according to the present disclosure is depicted.

[0021] Fig.10 Depicted is a functional block diagram of a TOF register module in accordance with an illustrative embodiment. DETAILED DESCRIPTION

[0022] The following merely illustrates the principles of the present disclosure. Therefore, it will be appreciated that those skilled in the art will be able to design various arrangements that, although not explicitly described or shown herein, implement the principles of the present disclosure and are included within its spirit and scope. More specifically, although many specific details are set forth, it is understood that embodiments of the present disclosure may be practiced without these specific details, and in other cases, well-known circuits, structures, and techniques are not shown in order not to obscure an understanding of the present disclosure.

[0023] Furthermore, all examples and conditional language recited herein are primarily and expressly intended to be used for teaching purposes only to help readers understand the principles of the present disclosure and the concepts contributed by the inventors to advance the art, and are to be construed as not being limited to such specifically recited examples and conditions.

[0024] In addition, all statements recording the principles, aspects and embodiments of the present disclosure and their specific examples are intended to cover both structural equivalents and functional equivalents thereof. In addition, such equivalents are intended to include both currently known equivalents and equivalents developed in the future (i.e., any element that performs the same function developed, regardless of structure).

[0025] Thus, for example, it will be appreciated by those skilled in the art that the diagrams herein represent conceptual views of illustrative structures embodying the principles of the present disclosure.

[0026] Additionally, those skilled in the art will appreciate that any flow charts, flowcharts, state transition diagrams, pseudocodes, and the like represent various processes that may be substantially represented in a computer-readable medium and thus executed by a computer or processor, whether or not such a computer or processor is explicitly shown.

[0027] In its claims, any element represented as a means for performing a specified function is intended to cover any manner of performing that function, including, for example, a) a combination of circuit elements that perform that function or b) software in any form, including firmware, microcode, etc., in combination with appropriate circuitry for executing that software to perform that function. The invention as defined by such claims resides in the fact that the functionality provided by the various recited components is combined and grouped together in the manner invoked by the claims. Applicants therefore recognize that any component that can provide these functions equivalent to those shown herein can be used. Finally, unless otherwise expressly indicated herein, the drawings are not drawn to scale.

[0028] The following terms are defined for use in this specification, including the appended claims:

[0029] · Detection area - also called field of view, is defined as the area of ​​interest that is imaged during an image frame;

[0030] · Image frame - also known as frame integration period (duration) and data integration period (duration), is defined as the period of time during which the detection area is imaged. An image frame typically includes multiple detection frames;

[0031] · Detection Frame - also called laser pulse period or light pulse period, is defined as the time period between light pulses emitted from the emitter; when used with reference to the time between GmAPD activation pulses, the frame period is usually used;

[0032] · Asynchronous arming is defined as the arming of a Geiger-mode avalanche photodiode of a pixel, independent of the arming of the Geiger-mode avalanche photodiodes of other pixels of the multi-pixel receiver;

[0033] · Asynchronous disarming is defined as the deactivation of the Geiger mode avalanche photodiode of a pixel, independent of the deactivation of the Geiger mode avalanche photodiodes of other pixels of the multi-pixel receiver;

[0034] · Multi-return capability is defined as the ability to detect more than one reflection of the same light pulse at a single pixel during a single detection frame.

[0035] By way of some additional background, first note that advances in LiDAR systems and methods have enabled practitioners to scan large areas while collecting billions of data points, each with precise latitude, longitude, and altitude (x,y,z) values ​​within a local (relative) coordinate system. This aggregation of billions of data points is called a point cloud dataset. Practitioners then extract object locations from the point cloud dataset and use this location information for subsequent decision making.

[0036] 1A-1B depict schematic diagrams of a TOF LiDAR system according to the prior art. System 100 is a GmAPD-based LiDAR system operable to collect one or more point cloud data sets to determine the state of a detection area surrounding it. As depicted in FIG. 1B , system 100 generally includes a transmitter 102, a receiver 104, and a processor 106.

[0037] The transmitter 102 provides an output signal 108 and includes a light source 118 and a transmitting optical device 120 for directing the output signal 108 toward a detection area 114. In operation, the transmitter 102 periodically transmits an interrogation signal including a series of light pulses 110 into the detection area (or field of view) 114. In the depicted example, the light source 118 is a diode laser that emits a series of light pulses 110 exhibiting a period T1 in response to a drive signal from the processor 106. The light pulses 110 have a wavelength and intensity suitable for interrogating the detection area. Typically, the wavelength of the light pulses 110 is in the range of approximately 900 nm to approximately 2000 nm; however, other usable wavelengths are known in the art.

[0038] As each light pulse 110 propagates through detection region 114 , object 116 may return a portion of the light energy of the light pulse toward receiver 104 as reflections 112 .

[0039] The receiver 104 includes a detector array 122 and receiving optics 124 for directing reflections 112 toward elements of the detector array 122. Each pixel of the detector array 122 includes a Geiger-mode avalanche photodiode (GmAPD) that can rapidly generate an electrical signal in response to detecting even a single photon when provided with a bias voltage equal to or greater than its breakdown voltage (i.e., when "activated") - thereby allowing sub-nanosecond precision photon time-of-flight measurements. When a pixel is activated, it can detect a low-intensity reflection 112 of a light pulse 110 and output an electrical signal to be detected and subsequently used by a processing system.

[0040] The processor 106 is a processing system and controller configured to provide control signals, strobe signals and timing signals to the transmitter 102 and the receiver 104, and to receive electrical signals from the receiver 104 and form a map of the detection area 114 based on the electrical signals. In general, the processor 106 includes a computer system for executing instructions according to the present disclosure, a memory (e.g., a computer readable medium such as volatile or non-volatile memory, etc.), one or more storage devices (e.g., flash memory, disk drives, optical disk devices, magnetic tape devices using magnetic, optical or other recording technologies, etc.), and an input / output structure that may include one or more transmitters, receivers and optical controls, optical transmitters, optical receivers, timing and control functions, filters, etc. The processor 106 can be a single-core or multi-core processor connected to other components of the system 100 via one or more buses.

[0041] As shown in FIG. 1A , the system 100 can be mounted on a movable platform such as a car. Although not specifically shown in FIG. 1A , such a LiDAR system can be mounted on a fixed or other mobile platform including land, sea, air, and / or spacecraft. In addition, such platforms can be configured or independently combined to sweep or scan over a large volume so that a complete 360-degree environmental view can be formed.

[0042] FIG2 depicts an illustrative timing diagram of multiple waveforms including a representative image frame for each pixel of a receiver of a conventional TOF LiDAR system, such as the TOF LiDAR system previously shown and described in FIG1A-1B. As seen in timing diagram 200, image frame 202 includes a plurality of substantially identical detection frames 204(1)-204(n) each exhibiting the same duration. In this illustrative example, the duration of each detection frame is equal to the duration of period T1 of the light pulse train of output signal 108.

[0043] For a given image frame, each individual detection frame 204(1), 204(2), ... 204(n) (collectively, detection frames 204) has a start time t0 that is synchronized with the emission of a respective light pulse of the interrogation signal. For example, light pulse 110(1) is emitted at time t0 of detection frame 204(1), light pulse 110(2) is emitted at time t0 of detection frame 204(2), and light pulse 110(n) is emitted at time t0 of detection frame 204(n). Note that in some embodiments, the start time of each detection frame may be different than the emission time of its respective light pulses, and the specific number of detection frames and light pulses may be different than that shown in this illustrative example.

[0044] At activation time ta, the processor 106 provides a gating signal to all GmAPD-based pixels of the receiver 104, wherein the gating signal controls the voltage at which each GmAPD is biased. In the depicted example, the gating signal raises the bias voltage of the GmAPD-based pixels from V1 to V2 at activation time ta, wherein V1 is a voltage lower than the threshold (i.e., breakdown) voltage of each GmAPD, and V2 is a voltage higher than the threshold voltage Vt. As a result, raising the bias voltage to V2 puts the pixels into Geiger mode, thereby activating them so that each pixel can detect the reception of a single photon of light. As shown in FIG. 2 , the activation time ta may occur at the end of a delay period. In the depicted example, in each detection frame, the delay period is very short, so that the activation time ta is only slightly delayed relative to the emission of its respective light pulse 110 at time t0. In some cases, a longer delay period is used in the detection frame so that the detector can selectively interrogate a portion of the detection area 114 that is located farther away from the system 100.

[0045] During operation, the gating signal remains high (i.e., at V2) throughout the gating period 206, thereby enabling the pixel to detect the arrival of a photon at any time during the gating period. At a deactivation time td, the gating period 206 ends for all pixels of the receiver 104, and at the deactivation time td, the gating signal decreases below the threshold voltage Vt to a voltage V1, thereby deactivating the GmAPD of the receiver 104. As will be understood and appreciated by those skilled in the art, the time between ta and td (i.e., the duration of the gating period) generally defines the area (range) of the detection region 114 scanned during each detection frame. When the gating signal decreases below the threshold voltage, the avalanche event occurring in the GmAPD stops (i.e., the avalanche current is quenched), thereby enabling the GmAPD to be reactivated at the beginning of the gating period 206 of the next detection frame.

[0046] As will be clear to those skilled in the art, typically, slightly prior to the end of each detection frame (as shown in FIG. 2 ), the GmAPD-based pixels of the receiver are deactivated, thereby defining a hold-off time 208 that allows trapped charge in the GmAPD to de-trap and recombine when the GmAPD is not in Geiger mode. As will be appreciated by those skilled in the art, such a hold-off time advantageously avoids false avalanche events such as dark counts due to follow-up pulses.

[0047] As described above, the pixel is able to detect reflection 112 arriving at any time during the strobe period 206. For example, in detection frames 204(1), 204(2), and 204(3), reflection 112 is received at times tr1, tr2, and trn, respectively, thereby triggering an avalanche detection event in the pixel's GmAPD driving its output signal high.

[0048] It should be noted that the pixels of the receiver 104 operate in a synchronous manner. In other words, they are activated and deactivated simultaneously during each detection frame.

[0049] While the physics of operation of GmAPD detectors is known and understood, it is important to note that uses of GmAPD detectors are typically not concerned with multiplication noise, but rather with detection probability - that is, the probability that an incident photon will produce a detection event. This probability is the product of the quantum efficiency, which is the probability that a photon will be absorbed in the active region of the device, and the avalanche probability, which is the probability that a photoelectron (or hole) will initiate an avalanche that does not terminate prematurely.

[0050] Additionally, it is noted that Geiger mode detection events provide no intensity information. The electrical pulses generated by the recombination of free carrier pairs resulting from the absorption of photons are indistinguishable from the electrical pulses generated by the recombination of free carrier pairs resulting from the de-trapping of trapped charge, the simultaneous absorption of many photons, or subsequent absorption of photons. As a result, as indicated in FIG. 2 , once an avalanche detection event is triggered by the first photon absorbed during a detection frame, the output signal of the pixel remains high until the GmAPD is quenched at the deactivation time td—regardless of whether additional photons are subsequently received. Therefore, each pixel of the detector array 122 can detect only one reflection in each detection frame, while for the remainder of the detection frame, the arrival of additional reflections is unaware. As a result, objects closer to the system 100 may obstruct or completely hide objects farther away. Advantageously, the methods, systems, and techniques disclosed herein mitigate this problem.

[0051] Figure 3A schematic diagram of an illustrative embodiment of a LiDAR system according to the present disclosure is depicted. System 300 is similar to system 100 described above; however, system 300 includes a receiver having multiple return capabilities by being configured such that multiple reflections from detection area 114 can be detected during any single detection frame. As a result, system 300 mitigates blockage and / or occlusion by objects within detection area 114. System 300 generally includes a transmitter 302, a receiver 304, and a processing system / controller 306.

[0052] Emitter 302 is similar to emitter 102 described above, and emits a series of light pulses 110 into a detection zone 114 .

[0053] The receiver 304 includes a detector 308 and receiving optics 124 for directing the reflections 112 to pixels of the detector 308 .

[0054] The processing system / controller 306 (hereinafter processor 306 ) is similar to the processor 106 described above; however, the processor 306 is also configured such that it can receive TOF data for multiple reflections within each detection frame and form a map of the detection area 114 based on the TOF data.

[0055] Figure 4 A schematic diagram of a detector according to an exemplary embodiment is depicted. The detector 308 is defined by the detector array 122 and the readout integrated circuit (ROIC) 310, and includes a pixel array 402 and a plurality of serial data readouts 406. In the depicted example, the pixel array 402 is a two-dimensional array of substantially identical pixels 404 including the GmAPD 502 and associated ROIC circuitry, wherein the pixels are arranged in 1×512 columns to achieve 64 pixels per output channel and 8 output channels, the output data 424 of which is read out via a separate serial data output 406.

[0056] As discussed in more detail below, each pixel 404 is configurable such that it can detect one or more reflections 112 of a light pulse 110 , store time-of-flight (TOF) information associated with the multiple reflections received during each detection frame, and provide the TOF information to processor 306 .

[0057] like Figure 4, pixel array 402 receives a plurality of global signals from processor 306, each global signal being provided to each pixel 404. Specifically, in the depicted example, pixel array 402 receives global signals including trigger signal 408, global activation 410, global deactivation 412, master clock 414, master clock enable 416, individual serial data clock 418, global holdoff time 420, and global activation time 422. In some embodiments, at least one of global signals 408 to 422 is provided to pixel array 402 by a circuit element other than processor 306, such as one or more controller circuits included in ROIC 310, a dedicated controller operably coupled to processor 306 and each of pixel array 402, or the like.

[0058] Figure 5 A functional block diagram of a detector pixel with multi-return capability is depicted in accordance with an illustrative embodiment. The pixel 404 includes a GmAPD 502 , a strobe signal controller 504 , a TOF counter 506 , and a TOF register module 508 .

[0059] The strobe signal controller 504 is an electronic circuit module operable to control whether the GmAPD 502 is in Geiger mode. The strobe signal controller 504 controls the state of the GmAPD 502 based on the APD signal 510 and a pair of global signals (i.e., the global holdoff time 420 and the global activation time 422) received from the processor 306. The strobe signal controller 504 is configured so that it can detect an avalanche detection event at the GmAPD 502, quench the avalanche quickly, and reactivate the GmAPD. As a result, the inclusion of the strobe signal controller enables multiple reflections to be detected by a single pixel during the same detection frame.

[0060] The TOF counter 506 is operable to maintain a running count of clock cycles on the master clock 414. The TOF counter 506 is reset via the master clock enable 416 at the beginning of each detection frame.

[0061] The TOF register module 508 includes a plurality of TOF registers and a control circuit for storing the count of the TOF counter 506 in a different TOF register each time a reflection 112 is detected at the GmAPD 502 in a detection frame, thereby enabling registration of time-of-flight information for each of the plurality of reflections 112 received at the GmAPD 502 during a single detection frame. The TOF register module 508 provides the stored TOF data for each reflection 112 detected during a single detection period to the processor 306 via a data output signal 516.

[0062] The ability to detect multiple reflections received at a pixel during a single detection frame and store TOF information for each reflection provides significant advantages over prior art TOF LiDAR systems according to embodiments of the present disclosure. To illustrate some of these advantages, an exemplary method for detecting one or more reflections at pixel 404 is presented here. It should be noted that the embodiments and methods described herein are only exemplary of some methods within the scope of the present disclosure, and countless alternative systems and methods are within the scope.

[0063] Figure 6 The operation of a method for interrogating a detection zone according to the present disclosure is depicted. The method 600 begins with operation 601, where the transmitter 102 transmits an output signal 108 toward the detection zone 114. As in the system 100 described above, in the depicted example, the output signal 108 includes a periodic sequence of n light pulses (i.e., light pulses 110-1 to 110-n) exhibiting a period T1. Figures 3 to 5 and Figures 7 to 10 Method 600 is described.

[0064] In operation 602, for each detection frame 802(i) (where i=1 to n), each pixel 404 is enabled to detect one or more reflections 112 from the detection area 114 within each detection frame 802(i). It should be noted that the detection frames 802(1) to 802(n) collectively define an image frame similar to the image frame 202.

[0065] Figure 7 Depicted are sub-operations of an exemplary sub-method suitable for enabling a pixel to detect multiple reflections during a single detection frame in accordance with the present disclosure.

[0066] Figure 8 A timing diagram of a representative detection frame for one pixel 404 according to sub-method 700 is depicted.

[0067] In sub-operation 701, processor 306 provides acquisition trigger signal 408 to pixel 404. As depicted in timing diagram 800, at start time t0, acquisition trigger signal 408 is provided for detection frame 802 (i). In the depicted example, acquisition trigger signal 408 is synchronized with the emission of light pulses 110 to detection region 114; however, such synchronization is not required. It should be noted that trigger signal 408 is a global signal provided to each pixel 404 of detector 308.

[0068] In sub-operation 702, at time t1, processor 306 provides an electrical pulse on global activation 410 to strobe signal controller 504. In response, strobe signal controller provides an electrical pulse on strobe signal 512, which activates GmAPD 502 to place it in Geiger mode. In the depicted example, as described above, time t1 is similar to activation time ta; therefore, GmAPD 502 is activated substantially at the same time as each light pulse 110 is emitted. However, it should be noted that these actions can be performed at different times. It should be noted that global activation 410 is also a global signal provided to each pixel 404 of detector 308.

[0069] The generation of the electrical pulse on global activation 410 defines the start of a range gate 804 during which the GmAPD 502 may be operable to detect reflections 112 .

[0070] In sub-operation 703, if Figure 8 As seen in FIG. 8 , at time tr-1, a first reflection 112-1 is received at the GmAPD 502. Receiving the reflection 112-1 causes an avalanche detection event that results in an electrical pulse on the APD signal 510. Those skilled in the art will recognize that a reflection may be received at the GmAPD 502 at any time within the detection frame 802(i).

[0071] The APD signal 510 is directed to the strobe signal controller 504 , the TOF counter 506 , and the TOF register module 508 .

[0072] In sub-operation 704, in response to the electrical pulse on APD signal 510, the value of TOF counter 506 at time tr-1 is captured and stored as TOF data 514-1 in the first TOF register in TOF register module 508. TOF data 514-1 serves as a TOF timestamp for reflection 112-1.

[0073] In sub-operation 705, in response to the electrical pulse on the APD signal 510, the strobe signal controller 504 deactivates the GmAPD 502 at time t2 by reducing the strobe signal 512 below the threshold voltage Vt. In the depicted example, the strobe signal controller 504 keeps the GmAPD 502 deactivated for a holdoff time 806, the duration of which is defined by the global holdoff time 420 and the global activation time 422. It should be noted that it is preferred to keep the global activation time as short as possible to minimize excessive crosstalk caused by avalanches during the activation period. It should also be noted that the delay between time tr-1 and t2 is typically very short, while in a manner similar to the holdoff time 208 described above and with respect to the system 100, the duration of the holdoff time 806 is selected to mitigate false counts due to follow-up pulses of the GmAPD 502.

[0074] In sub-operation 706 , the strobe signal controller 504 reactivates the GmAPD 502 at the end of the hold-off time 806 (ie, at time t3 ) by increasing the level of the strobe signal 512 above the threshold Vt of the GmAPD.

[0075] The functional sequence of sub-operations 703 to 706 is then repeated to detect subsequent reflections 112 - 2 to 112 - m , where m is the total number of reflections 112 incident on the GmAPD 502 during the gating period 804 .

[0076] For example, Figure 8 As depicted in FIG. 5 , at an arbitrary time tr-2, a second reflection 112-2 is received at the GmAPD 502, which causes a second avalanche detection event resulting in a second electrical pulse on the APD signal 510. The value of the TOF counter 506 at time tr-2 is captured as TOF data 514-2 and stored in a different TOF register in the TOF register module 510 as the TOF timestamp of the reflection 112-2. The GmAPD 502 is then quenched again at time t4 and reactivated at time t5 after a holdoff time 806.

[0077] In the depicted example, during the detection frame 802 (i), only two reflections 112 are detected at the pixel 404 (i.e., m=2). However, it should be clear to those skilled in the art that m can have any value from 0 to n without departing from the scope of the present disclosure. In practice, the value of m is limited only by the number of TOF registers included in the TOF register module 508, the duration of the range gate 804, and the length of the holdoff time 806 required to mitigate false counts due to follow-up pulses in the GmAPD 502. In the depicted example, n=3, the range gate 804 is approximately 2 microseconds, and the holdoff time 806 is approximately 0.5 microseconds.

[0078] In sub-operation 707, processor 306 provides global deactivation 412 to strobe signal controller 504 at time t6, which defines the end of range gating 804. In response, strobe signal controller deactivates GmAPD 502 by reducing strobe signal 512 below threshold voltage Vt. Typically, time t6 is slightly prior to the end of detection frame 802(i), thereby establishing holdoff time 808 for all pixels 404 of the pixel array. Similar to hold time 208 described above, holdoff time 808 allows trapped charge in the GmAPD to de-capture and recombine before the start of the next detection frame, thereby advantageously avoiding false avalanche events such as dark counts due to follow-up pulses.

[0079] After the global deactivation 412 takes effect, any ongoing holdoff time 806 expires.

[0080] It should be noted that similar to the pixels of the receiver 104 described above, all pixels 404 of the receiver 308 are synchronously activated at the beginning of each range strobe 804 and synchronously deactivated at the end of each range strobe 804 via global activation 410 and global deactivation 412, respectively. However, the inclusion of a strobe signal controller 504 within each pixel enables each pixel to be deactivated, quenched, and reactivated several times within a range strobe 804, independent of the operation of any other pixel 404 within the receiver 308. In other words, the pixels 404 are configured such that they can be asynchronously deactivated and asynchronously reactivated during the range strobe of each detection frame 802.

[0081] Returning now to method 600, in operation 603, TOF data 514-1 through 514-m are read out to processor 306 as data output 516. Typically, the TOF data is read out in response to the assertion of global deactivation 412 at time t6.

[0082] In operation 604 , the processor 306 calculates the range of any object 116 identified in the detection area 114 , wherein the range of such an object is estimated based on the data output signal 516 received from each pixel 404 .

[0083] Fig. 9 An exemplary circuit arrangement of a strobe signal controller according to the present disclosure is depicted.The strobe signal controller 504 includes a holdoff timer 902, an activation timer 904, a bias controller 906, and conventional summing nodes 908-1 and 908-2.

[0084] The holdoff timer 902 is a conventional programmable digital counter that tracks the clock cycles on the master clock 414. In response to receiving an electrical pulse on the APD signal 510, the holdoff timer 902 holds the holdoff signal 910 low for a holdoff period based on a global holdoff time 420. The global holdoff time 420 is typically received from the processor 306 or stored in a configuration register included in the ROIC 310. The holdoff timer 902 is included in the pixel 404 to keep the GmAPD 502 in a deactivated state for a period of time after an avalanche detection event to allow trapped charge in its active region to recombine before the GmAPD is reactivated. Therefore, including the holdoff timer 902 mitigates false alarms generated in the system 300 due to follow-up pulses in one or more pixels 404.

[0085] The activation timer 904 is a conventional programmable digital counter configured to provide an activation signal 912 to the bias controller 906. The activation timer 904 asserts the activation signal 912 upon expiration of the holdoff period of the holdoff timer 902 or upon assertion of the global activation 410, the combination of which is received from the summing node 908-1 at the holdoff timer 902. The activation period of the activation timer 904 is based on the global activation time 422, which is typically provided by the processor 306 or stored in a configuration register included in the ROIC 310.

[0086] The bias controller 906 is a circuit configured to control the bias voltage applied to the GmAPD 502 via the strobe signal 512. The bias controller 906 receives the activation signal 912 from the activation timer 904 and receives the deactivation signal 914 from the summing node 908-2. The deactivation signal 914 is a combination of the APD signal 510 and the global deactivation 412, such that the assertion of one or both of these signals causes the deactivation signal 914 to be asserted.

[0087] The bias controller 906 activates the GmAPD 502 in response to the assertion of the activation signal 912 and deactivates the GmAPD in response to the assertion of the deactivation signal 914 .

[0088] The gating signal controller 504 is configured to deactivate the GmAPD 502 in response to (1) the assertion of the global deactivation 412 or (2) the detection of a reflection 112 at the GmAPD 502, the detection of the reflection 112 causing an electrical pulse on the APD signal 510. In response to the detection of the reflection, the holdoff timer 902 initiates the holdoff time 806 to ensure that the avalanche detection event initiated by the absorption of the reflection is completely quenched and substantially all trapped charge becomes released before the GmAPD is reactivated. Alternatively, in response to the global deactivation 412, the holdoff timer does not initiate the holdoff time, but direct quenching is applied to the GmAPD for the duration of the global deactivation signal. This is typically applied at the end of the range gating sequence to cause all GmAPDs of the pixel array 402 to be in a deactivated state at the end of the detection frame 802.

[0089] The strobe signal controller 504 is also configured to automatically place the GmAPD 502 into the Geiger mode in response to (1) the assertion of the global activation 410 or (2) upon expiration of the holdoff period of the holdoff timer 902 .

[0090] It should be noted that Fig. 9 As depicted in FIG. 5 , the strobe signal controller 504 is merely one example of a suitable configuration within the scope of the present disclosure.

[0091] Fig.10 1002A and 1002B, a controller 1004 and a serial output multiplexer 1006 .

[0092] Each of the TOF register groups 1002A and 1002B (hereinafter referred to as groups 1002A and 1002B) includes substantially identical TOF registers 1008 - 1 to 1008 - n (collectively referred to as TOF registers 1008 ).

[0093] Groups 1002A and 1002B are operably coupled to controller 1004 so that TOF data for a current detection frame can be read into one of groups 1002A and 1002B while the other group holds TOF data from a previous detection frame.

[0094] Groups 1002A and 1002B are also operably coupled to a serial output multiplexer 1006 , which enables the TOF data stored in their registers to be serially read out to processor 306 as data output 516 .

[0095] Controller 1004 is a circuit controller for receiving TOF data 514 from TOF counter 506 and storing TOF data in one of TOF register groups 1002A and 1002B. Controller 1004 is configured to exchange the functions of groups 1002A and 1002B between capture and readout, thereby enabling the "integrate when reading" capability. In other words, TOF register module 508 can read out TOF data from the previous detection frame while TOF data of the current detection frame is being stored. The capture and readout functions of groups 1002A and 1002B are controlled by group selection signal 1010.

[0096] The serial output multiplexer 1006 is a conventional serial peripheral interface (SPI) and is operable to serially read out the TOF data stored in the TOF register 1008 of one of the banks 1002A and 1002B as determined by the bank select signal 1010 from the controller 1004 .

[0097] It should be noted that Fig.10 As depicted in FIG. 5 , the TOF register module 508 is only one example of a suitable configuration of a TOF register module within the scope of the present disclosure. For example, in some embodiments, only one TOF register set is included in the TOF register module 508. In some embodiments, more than two TOF register sets are included in the TOF register module 508.

[0098] It is to be understood that this disclosure teaches only some examples of embodiments of the invention and that after reading this disclosure, those skilled in the art may easily conceive of many variations of the invention and that the scope of the invention will be determined by the appended claims.

Claims

1. A light detection and ranging LiDAR system, comprising: a light source for emitting a series of light pulses toward a detection region, wherein the light pulses in the series of light pulses are periodic and separated by a period T1; and a receiver comprising a plurality of pixels for detecting reflection of a light pulse during each of a plurality of detection frames, each detection frame having a duration based on T1 and having a start time based on emission of a different light pulse in the series of light pulses, wherein each pixel comprises: (i) Geiger mode avalanche photodiode GmAPD; (ii) a gate signal controller operable to asynchronously activate and asynchronously deactivate the GmAPD, wherein the gate signal controller provides a gate signal to the GmAPD, and wherein the GmAPD is activated and in a Geiger mode when the gate signal is in an active state, and is deactivated and out of the Geiger mode when the gate signal is in an inactive state; (iii) a time-of-flight (TOF) counter for tracking the time between emission of a light pulse in the series of light pulses and detection of one or more reflections of the light pulse in the series of light pulses; and (iv) a TOF register module for storing TOF data associated with the one or more reflections of the light pulses in the series of light pulses; The LiDAR system is characterized in that each pixel has a multiple return capability, wherein each pixel is arranged to: receive a first reflection of a first light pulse in the series of light pulses during a first detection frame in the multiple detection frames, so that receiving the first reflection triggers a first avalanche detection event; asynchronously deactivate the corresponding GmAPD to quench the first avalanche detection event; and asynchronously activate the corresponding GmAPD to initiate a second avalanche detection event in response to receiving a second reflection of the first light pulse in the series of light pulses during the first detection frame, so that the receiver is configured so that it is operable to detect multiple reflections of each light pulse in the series of light pulses during each detection frame in the multiple detection frames. 2 . The system of claim 1 , further comprising a processor configured to form a detection area map based on TOF data stored in the TOF register module of at least one pixel among the plurality of pixels.

3. The system according to claim 2, wherein: The processor is further configured to provide at least one global signal to all pixels of the plurality of pixels, wherein the global signal is selected from the group consisting of a global activation signal, a global deactivation signal, and a master clock.

4. The system according to claim 1, wherein: The strobe signal controller is operable to deactivate the corresponding GmAPD of the strobe signal controller in response to any one of (1) detecting a reflection by the corresponding GmAPD of the strobe signal controller and (2) a global deactivation signal received at each pixel of the plurality of pixels.

5. The system according to claim 4, wherein: The strobe signal controller comprises: a holdoff timer configured to generate a holdoff signal in response to assertion of an APD signal from the GmAPD; an activation timer that asserts an activation signal in response to assertion of at least one of the holdoff signal and a global activation signal, wherein the global activation signal is received at each pixel of the plurality of pixels; a summing node that combines the APD signal with a global deactivation signal as a deactivation signal, the global deactivation signal being received at each pixel in the plurality of pixels; and A bias controller is operable to provide a strobe signal, wherein the bias controller provides the strobe signal in an asserted state in response to the assertion of the activation signal and provides the strobe signal in an inactive state in response to the assertion of the deactivation signal.

6. The system according to claim 1, wherein: The TOF register module includes: a first TOF register set, the first TOF register set comprising a first plurality of TOF registers; a second TOF register set, the second TOF register set comprising a second plurality of TOF registers; and A controller operable to enable TOF data to be stored in one of the first register set and the second register set, while enabling TOF data to be read out from the other of the first register set and the second register set.

7. A method for estimating the range of at least one object in a detection area, the method comprising: emitting a series of light pulses toward the detection region, wherein the light pulses in the series of light pulses are periodic and separated by a period T1; defining a plurality of detection frames having a duration T1, wherein each detection frame has a start time based on emission of a different light pulse in the series of light pulses; receiving a first reflection of a first light pulse in the series of light pulses at a first pixel of a receiver during a first detection frame in the plurality of detection frames, wherein the first pixel comprises a first Geiger mode avalanche photodiode GmAPD, and wherein receiving the first reflection triggers a first avalanche detection event; asynchronously deactivating the first GmAPD to quench the first avalanche detection event; and in response to receiving a second reflection of the first light pulse in the series of light pulses during the first detection frame, asynchronously activating the first GmAPD to initiate a second avalanche detection event, wherein a gating signal is provided to the first GmAPD to asynchronously activate and asynchronously deactivate the first GmAPD, and wherein, when the gating signal is in an effective state, the first GmAPD is activated and is in a Geiger mode, and when the gating signal is in an ineffective state, the first GmAPD is deactivated and leaves the Geiger mode.

8. The method of claim 7, further comprising deactivating the first GmAPD and a second GmAPD included in a second pixel of the receiver, wherein: The first GmAPD and the second GmAPD are synchronously deactivated at a first time, the first time being based on a start time of a second detection frame among the plurality of detection frames. 9 . The method of claim 8 , further comprising synchronously activating the first GmAPD and the second GmAPD at a second time, the second time being based on a start time of the second detection frame.

10. The method of claim 7, further comprising estimating a range of a first object in the detection zone based at least in part on a time between emission of the first light pulse and receipt of the first reflection.

11. The method according to claim 7, further comprising: storing a first time-of-flight (TOF) value in a first TOF register, the first TOF value being based on a first delay between emission of the first light pulse and receipt of the first reflection at the first GmAPD; as well as A second TOF value is stored in a second TOF register, the second TOF value being based on a second delay between emission of the first light pulse and receipt of a second reflection at the first GmAPD during the first detection frame.

12. The method according to claim 11, further comprising: storing a third TOF value in a third TOF register, the third TOF value being based on a third delay between emission of a second light pulse in the series of light pulses and receipt of a third reflection at the first GmAPD during a second detection frame in the plurality of detection frames; storing a fourth TOF value in a fourth TOF register, the fourth TOF value being based on a fourth delay between emission of the second light pulse and receipt of a fourth reflection at the first GmAPD during the second detection frame; as well as The first TOF value and the second TOF value are provided to a processor while the third TOF value and the fourth TOF value are being stored.

13. A light detection and ranging LiDAR system comprising: a light source configured to emit a series of light pulses toward a detection region, wherein the light pulses in the series of light pulses are periodic and separated by a period T1; a receiver comprising a plurality of pixels for detecting reflection of the light pulse during each of a plurality of detection frames, each detection frame having a duration based on T1 and having a start time based on emission of a different light pulse in the series of light pulses, wherein each pixel comprises: (i) Geiger mode avalanche photodiode GmAPD; (ii) a gating signal controller operable to asynchronously activate and asynchronously deactivate the GmAPD; (iii) a counter for determining a delay between emission of each light pulse in the series of light pulses and receipt of each reflection of a plurality of reflections of the light pulse at the pixel; and (iv) a plurality of time-of-flight (TOF) registers for storing TOF data corresponding to each of the plurality of reflections, The LiDAR system is characterized in that each pixel has a multiple return capability, wherein each pixel is arranged to: receive a first reflection of a first light pulse in the series of light pulses during a first detection frame in the multiple detection frames, so that receiving the first reflection triggers a first avalanche detection event; asynchronously deactivate the corresponding GmAPD to quench the first avalanche detection event; and asynchronously activate the corresponding GmAPD to initiate a second avalanche detection event in response to receiving a second reflection of the first light pulse in the series of light pulses during the first detection frame, so that the receiver is configured so that it is operable to detect multiple reflections of each light pulse in the series of light pulses during each detection frame in the multiple detection frames.

14. The system of claim 13, further comprising a processor operable to form a detection area map based on TOF data stored in the TOF register module of at least one pixel among the plurality of pixels.

15. The system of claim 13, wherein: The receiver is configured such that the plurality of GmAPDs can be synchronously activated at a first time based on the start of each of the plurality of detection frames, and can be synchronously deactivated at a second time based on the emission of a next light pulse in the series of light pulses.

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