LIDAR SYSTEM INCLUDING Geiger-MODE Avalanche Photodiode-BASED RECEIVER WITH PIXELS WITH MULTI-RETURN

Abstract

A Geiger mode avalanche photodiode-based LiDAR system and method that interrogates a detection region with a periodic series of light pulses is disclosed. Reflections of the periodic series of light pulses are detected via a receiver that includes 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 reflection. As a result, each pixel may detect multiple reflections of the same light pulse during a single detection frame whose duration is defined by the periodicity of a series of light pulses. Further, each pixel may store time-of-flight data for each of a plurality of reflections detected during the detection frame. Thus, once each individual pixel of the receiver detects the first reflection, each individual pixel of the receiver is not unperceived and inoperable for the remainder of the detected frame.

Description

[0001] This application is a divisional application of the patent application with the application date of October 19, 2020, the application number of 2020800791730, and the invention name of "LIDAR system of a receiver based on Geiger-mode avalanche photodiodes including pixels with multiple return capabilities". Technical Field

[0002] The present disclosure generally relates to scanning optical ranging and detection systems and methods, and more particularly, to time-of-flight optical detection and ranging (LiDAR) systems and methods employing Geiger-mode avalanche photodiodes. Background Art

[0003] Optical detection and ranging (LiDAR) systems enable the measurement of the distance to 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) towards 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, which represents the time 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 driverless vehicles, agricultural equipment, and the like. Summary of the Invention

[0004] Advances have been made in the art according to some aspects of the present disclosure related to 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.

[0005] As with systems and methods of the prior art, embodiments in accordance with the present disclosure use a pulsed laser and a receiver to interrogate a detection region, the receiver including a pixel array in which each pixel includes a Geiger mode avalanche photodiode. The pulsed laser directs a periodic series of optical pulses into the detection region, and the receiver detects reflections of the optical pulses from objects 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 optical pulse. When at least some of the optical pulses reflect from an object within the detection region back to a pixel of the detector, an avalanche detection event is triggered at the avalanche photodiode of that pixel, and the range to the object is estimated based on the time between the emission of the optical pulse and the occurrence of the avalanche detection event (i.e., the time of flight of one or more photons included in the reflection). Unfortunately, in prior art TOF LiDAR systems, once an avalanche detection event is triggered during a detection frame, that pixel becomes 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 per detection frame and is unaware of the remainder of any detection frame in which a reflection has been detected.

[0006] In stark contrast to the prior art, a LiDAR system in accordance with the present disclosure includes a receiver whose pixels include circuitry enabling 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 has detected one reflection, it is not unaware of the remainder of the detection frame. The circuitry included in each pixel enables its Geiger mode avalanche photodiode to be automatically reset asynchronously after each avalanche detection event, so that it can be quickly deactivated to stop the avalanche event and then reactivated so that it can detect another reflection. Each pixel also includes a plurality of registers for holding a timestamp associated with each avalanche detection event occurring within a single detection frame, wherein each timestamp indicates the round-trip time of flight of the optical pulse between the LiDAR system and the object from which the reflection was received.

[0007] An exemplary embodiment in accordance with the present disclosure is a TOF LiDAR system including: a source for emitting a periodic series of optical pulses toward a detection field; a receiver for detecting reflections from the detection region; and a processor for providing a gating signal and a control signal to the source and the receiver and for estimating the range of one or more objects in the detection region based on TOF data received from the receiver.

[0008] The receiver includes: a pixel array, where each pixel in the pixel array includes a Geiger-mode avalanche photodiode for detecting reflections from a detection area; a strobe signal controller that automatically deactivates and reactivates the GmAPD after an avalanche detection event in response to the absorption of a reflection to enable detection of subsequent reflections; a TOF counter that tracks the time between the emission of an optical pulse and the detection of the reflection of the optical pulse; and a TOF register module that stores TOF data associated with multiple reflections detected by the GmAPD during a single detection frame.

[0009] In some embodiments, the strobe signal controller includes a hold-off timer and an activation timer. Upon detection of an avalanche detection event, the hold-off timer initiates the automatic, asynchronous deactivation and quenching of the GmAPD. The activation timer initiates the asynchronous reactivation of the GmAPD in response to a signal from the hold-off timer, or initiates the synchronous activation of the GmAPD in response to a global activation signal from a processor.

[0010] In some embodiments, the TOF register module includes two register banks and a controller. One register bank includes multiple TOF registers for storing the time-of-flight information of reflections detected during an active detection frame, and the second bank includes TOF registers for reading out the time-of-flight information of reflections detected during the previous detection frame.

[0011] Embodiments in accordance with the present disclosure include a light detection and ranging (LiDAR) system. The light detection and ranging (LiDAR) system includes: a light source configured to emit a series of light pulses towards a detection area, wherein the light pulses in the series of light pulses are periodic and separated by a period T1; and a receiver including a plurality of pixels configured to detect reflections of the light pulses during each of 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 includes: (i) a Geiger mode avalanche photodiode (GmAPD) configured to detect reflections of light pulses from the detection area; (ii) a gating signal controller configured to activate the GmAPD to place it in Geiger mode and deactivate the GmAPD to take it out of Geiger mode; (iii) a counter configured to track the time of flight (TOF) between the emission of a light pulse in the 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 configured to store TOF data associated with one or more reflections of a light pulse in the series of light pulses; wherein the LiDAR system is characterized in that each pixel of the receiver is configured such that it is operable to detect multiple reflections of each light pulse in the series of light pulses during each of the plurality of detection frames.

[0012] Another embodiment in accordance with the present disclosure is a method for estimating the range of at least one object in a detection area. The method includes: emitting a series of light pulses towards 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 of 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 the receiver during a first detection frame of 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

[0013] Figures 1A to 1B A schematic diagram of a TOF LiDAR system according to the prior art is depicted.

[0014] FIG. 2 depicts an example including such as previously in Figures 1A to 1BExemplary timing diagrams of multiple waveforms of a representative image frame of a pixel of a receiver of a TOF LiDAR system, such as the TOF LiDAR system shown and described herein.

[0015] Figure 3 Schematic diagram depicting an exemplary embodiment of a LiDAR system in accordance with the present disclosure.

[0016] Figure 4 Schematic diagram depicting a detector in accordance with an exemplary embodiment.

[0017] Figure 5 Functional block diagram depicting a detector pixel in accordance with an exemplary embodiment.

[0018] Figure 6 Depicts the operation of a method for interrogating a detection region in accordance with the present disclosure.

[0019] Figure 7 Depicts sub-operations of an example sub-method suitable for enabling a pixel to detect multiple reflections during a single detection frame in accordance with the present disclosure.

[0020] Figure 8 Timing diagram depicting a representative detection frame of a pixel 404 in accordance with sub-method 700.

[0021] Figure 9 Depicts an exemplary circuit arrangement of a gating-signal controller in accordance with the present disclosure.

[0022] Figure 10 Functional block diagram depicting a TOF register module in accordance with an exemplary embodiment. Detailed Description

[0023] The following merely illustrates the principles of the present disclosure. Accordingly, it will be understood 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 fall within its spirit and scope. More specifically, while numerous specific details are set forth, it is to be understood that embodiments of the present disclosure may be practiced without these specific details, and in other instances, well-known circuits, structures, and techniques have not been shown so as not to obscure the understanding of the present disclosure.

[0024] In addition, all example and conditional language recited herein is expressly intended solely for pedagogical purposes to aid the reader in understanding the principles of the present disclosure and the concepts contributed by the inventor to advance the art, and is to be construed as not being limited to such specifically recited examples and conditions.

[0025] In addition, all statements that recite the principles, aspects, and embodiments of the present disclosure, as well as specific examples thereof, are intended to cover both their structural equivalents and functional equivalents. Additionally, such equivalents are intended to include both currently known equivalents and equivalents developed in the future (i.e., any elements developed to perform the same function regardless of structure).

[0026] Thus, for example, those skilled in the art will understand that the diagrams herein represent a conceptual view of an exemplary structure implementing the principles of the present disclosure.

[0027] Furthermore, those skilled in the art should understand that any flowchart, flow diagram, state transition diagram, pseudocode, etc. represents various processes that can 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.

[0028] In its claims, any element expressed as a means for performing a specified function is intended to cover any way of performing that function, including, for example, a) a combination of circuit elements that perform that function or b) any form of software, including firmware, microcode, etc., that incorporates suitable circuitry for executing the software to perform that function. The invention as defined by such claims lies in the fact that the functions provided by the various recited elements are combined and brought together in the manner called for by the claims. Accordingly, the applicant believes that any element that can provide functions equivalent to those shown herein can be provided. Finally, unless explicitly stated otherwise herein, the drawings are not drawn to scale.

[0029] The following terms are defined for use in this specification, including the appended claims:

[0030] · Detection region - also referred to as the field of view, is defined as the area of interest that is imaged during an image frame;

[0031] · Image frame - also referred to as the frame integration period (duration) and data integration period (duration), is defined as the time period during which the detection region is imaged. An image frame typically includes a plurality of detection frames;

[0032] · Detection frame - also referred to as the laser pulse period or optical pulse period, is defined as the time period between the emission of optical pulses from a transmitter; when used with reference to the time between GmAPD activation pulses, the frame period is typically used;

[0033] · Asynchronous arming is defined as the activation of the Geiger mode avalanche photodiodes of pixels independently of the activation of the Geiger mode avalanche photodiodes of other pixels of a multi-pixel receiver;

[0034] · Asynchronous disarming is defined as the disarming of the Geiger-mode avalanche photodiodes of the pixels, independent of the disarming of the Geiger-mode avalanche photodiodes of other pixels of the multi-pixel receiver;

[0035] · Multiple return capability is defined as the ability to detect more than one reflection of the same optical pulse at a separate pixel during a single detection frame.

[0036] With some additional background, first note that advancements 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 referred to as a point cloud dataset. Practitioners then extract object positions from the point cloud dataset and use this position information for subsequent decision-making.

[0037] Figures 1A to 1B A schematic diagram of a TOF LiDAR system according to the prior art is depicted. System 100 is a GmAPD-based LiDAR system operable to collect one or more point cloud datasets to determine the state of the detection area surrounding it. As Figure 1B depicted, system 100 generally includes a transmitter 102, a receiver 104, and a processor 106.

[0038] The transmitter 102 provides an output signal 108 and includes a light source 118 and transmitting optics 120 for directing the output signal 108 towards the detection area 114. In operation, the transmitter 102 periodically emits an interrogation signal including a series of optical 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 optical pulses 110 exhibiting a period T1 in response to a drive signal from the processor 106. The optical pulses 110 have a wavelength and intensity suitable for interrogating the detection area. Generally, the wavelength of the optical pulses 110 is in the range of approximately 900 nm to approximately 2000 nm; however, other wavelengths known in the art may also be used.

[0039] As each optical pulse 110 propagates through the detection area 114, an object 116 may return a portion of the optical energy of the optical pulse towards the receiver 104 as a reflection 112.

[0040] The receiver 104 includes a detector array 122 and receiving optics 124 for directing the reflection 112 towards the elements of the detector array 122. Each pixel of the detector array 122 includes a Geiger-mode avalanche photodiode (GmAPD), which can rapidly generate an electrical signal in response to detecting even a single photon when the Geiger-mode avalanche photodiode is provided with a bias voltage equal to or greater than its breakdown voltage (i.e., when “activated”) - thereby allowing photon time-of-flight measurements with sub-nanosecond precision. When a pixel is activated, it can detect the low-intensity reflection 112 of the light pulse 110 and output an electrical signal to be detected and subsequently used by the processing system.

[0041] The processor 106 is a processing system and controller configured to provide control signals, gating signals, and timing signals to the transmitter 102 and the receiver 104, receive electrical signals from the receiver 104, and form a map of the detection region 114 based on the electrical signals. Generally, 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), one or more storage devices (e.g., flash memory, disk drives, optical disc devices, tape devices employing magnetic, optical, or other recording technologies), 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.

[0042] As Figure 1A shown, the system 100 can be mounted on a movable platform such as an automobile. Although not specifically shown Figure 1A herein, such a LiDAR system can be mounted on a fixed or other movable platform including land, sea, air, and / or space vehicles. Additionally, such platforms can be configured or combined independently to sweep or scan over a large volume such that a complete 360-degree view of the environment can be formed.

[0043] FIG. 2 depicts an exemplary timing diagram of multiple waveforms of a representative image frame of each pixel of a receiver of a conventional TOF LiDAR system including a TOF LiDAR system such as that previously shown and described Figures 1A to 1B herein. As seen in the timing diagram 200, the image frame 202 includes a plurality of substantially identical detection frames 204(1) to 204(n) each exhibiting the same duration. In this exemplary example, the duration of each detection frame is equal to the duration of the period T1 of the light pulse sequence of the output signal 108.

[0044] For a given image frame, each individual detection frame 204(1), 204(2), … 204(n) (collectively referred to as detection frames 204) has a start time t0, which is synchronized with the emission of each optical pulse of the interrogation signal. For example, optical pulse 110(1) is emitted at time t0 of detection frame 204(1), optical pulse 110(2) is emitted at time t0 of detection frame 204(2), and optical 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 can be different from the emission time of its respective optical pulses, and the specific number of detection frames and optical pulses can be different from the number shown in this illustrative example.

[0045] At activation time ta, the processor 106 provides a gating signal to all GmAPD-based pixels of the receiver 104, where the gating signal controls the voltage that biases each GmAPD. In the depicted example, the gating signal raises the bias voltage of the GmAPD-based pixels from V1 to V2 at activation time ta, where 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 places the pixels in Geiger mode, thereby activating them such that each pixel can detect the reception of a single photon of light. As shown in FIG. 2, the activation time ta can occur at the end of a delay period. In the depicted example, in each detection frame, this delay period is very short such that the activation time ta is only slightly delayed relative to the emission of its respective optical pulses 110 at time t0. In some cases, a longer delay period is used in the detection frame such that the detector can selectively interrogate portions of the detection region 114 that are located further away from the system 100.

[0046] During operation, throughout the gating period 206, the gating signal remains high (i.e., at V2), thereby enabling the pixels to detect the arrival of photons at any time during the gating period. At deactivation time td, for all pixels of the receiver 104, the gating period 206 ends, and at deactivation time td, the gating signal is reduced below the threshold voltage Vt to voltage V1, thereby deactivating the GmAPDs 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 (extent) of the detection region 114 scanned during each detection frame. When the gating signal is reduced below the threshold voltage, the avalanche events occurring in the GmAPDs stop (i.e., the avalanche current quenches), thereby enabling the GmAPDs to be reactivated at the start of the gating period 206 of the next detection frame.

[0047] As will be clear to those skilled in the art, typically, slightly before 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 charges in the GmAPD to be detrapped and recombine when the GmAPD is not in Geiger mode. As will be appreciated by those skilled in the art, this hold-off time advantageously avoids spurious avalanche events such as dark counts due to following pulses.

[0048] As described above, the pixels are capable of detecting reflections 112 that arrive at any time during the gating period 206. For example, in detection frames 204(1), 204(2), and 204(3), reflections 112 are received at times tr1, tr2, and trn, respectively, triggering avalanche detection events in the GmAPD of the pixel that drives its output signal high.

[0049] It should be noted that the pixels of receiver 104 operate in a synchronous manner. In other words, they are simultaneously activated and deactivated during each detection frame.

[0050] Although the operating physics of GmAPD detectors are known and understood, it should be noted that the use of GmAPD detectors generally does not focus on multiplication noise, but rather on the detection probability - i.e., the probability that an incident photon will produce a detection event. This probability is the product of the quantum efficiency and the avalanche probability, where the quantum efficiency is the probability that a photon will be absorbed in the active region of the device, and the avalanche probability is the probability that a photoelectron (or hole) will initiate an avalanche that does not terminate prematurely.

[0051] Furthermore, it should be noted that Geiger mode detection events do not provide intensity information. The electrical pulses generated by the recombination of free carrier pairs resulting from the absorption of photons are indistinguishable from those generated by the recombination of free carrier pairs resulting from the detrapping of trapped charges, the simultaneous absorption of many photons, or subsequently absorbed photons. As a result, as indicated in FIG. 2, once an avalanche detection event is triggered by the first absorbed photon during a detection frame, the output signal of the pixel remains high until the GmAPD quenches at the deactivation time td - regardless of whether additional photons are subsequently received. Thus, each pixel of detector array 122 can only detect one reflection in each detection frame, and for the remainder of that detection frame, is unaware of the arrival of additional reflections. As a result, an object closer to system 100 may obscure or completely hide a more distant object. Advantageously, the methods, systems, and techniques according to the present disclosure mitigate this problem.

[0052] Figure 3Depicts a schematic diagram of an exemplary embodiment of a LiDAR system in accordance with the present disclosure. System 300 is similar to system 100 described above; however, system 300 includes a receiver having multiple return capabilities configured to enable detection of multiple reflections from detection region 114 during any single detection frame. As a result, system 300 alleviates blocking and / or occlusion of objects within detection region 114. System 300 generally includes a transmitter 302, a receiver 304, and a processing system / controller 306.

[0053] Transmitter 302 is similar to transmitter 102 described above and emits a series of light pulses 110 into detection region 114.

[0054] Receiver 304 includes a detector 308 and receiving optics 124 for directing reflections 112 to the pixels of detector 308.

[0055] Processing system / controller 306 (hereinafter referred to as processor 306) is similar to processor 106 described above; however, processor 306 is further configured to be able to receive TOF data of multiple reflections within each detection frame and form a map of detection region 114 based on the TOF data.

[0056] Figure 4 Depicts a schematic diagram of a detector in accordance with an exemplary embodiment. Detector 308 is jointly defined by a detector array 122 and a readout integrated circuit (ROIC) 310 and includes a pixel array 402 and a plurality of serial data readers 406. In the depicted example, pixel array 402 is a two-dimensional array of substantially identical pixels 404 including GmAPD 502 and associated ROIC circuitry, where the pixels are arranged in 1×512 columns to achieve 64 pixels per output channel and 8 output channels, and the output data 424 of the output channels is read out via separate serial data outputters 406.

[0057] As discussed in more detail below, each pixel 404 is configurable such that it can detect one or more reflections 112 of light pulse 110, store time-of-flight (TOF) information associated with the multiple reflections received during respective detection frames, and provide the TOF information to processor 306.

[0058] As Figure 4As indicated, pixel array 402 receives a plurality of global signals from processor 306, and each global signal is 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 blanking 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 circuit elements other than processor 306, such as one or more controller circuits included in ROIC 310, a dedicated controller operably coupled to each of processor 306 and pixel array 402, etc.

[0059] Figure 5 A functional block diagram of a detector pixel having multiple return capabilities according to an exemplary embodiment is depicted. Pixel 404 includes GmAPD 502, a strobe signal controller 504, a TOF counter 506, and a TOF register module 508.

[0060] Strobe signal controller 504 is an electronic circuit module operable to control whether GmAPD 502 is in Geiger mode. Strobe signal controller 504 controls the state of GmAPD 502 based on APD signal 510 and a pair of global signals received from processor 306 (i.e., global blanking time 420 and global activation time 422). Strobe signal controller 504 is configured such that it can detect an avalanche detection event at GmAPD 502, quickly quench the avalanche, and reactivate GmAPD. As a result, including the strobe signal controller enables multiple reflections to be detected by a single pixel during the same detection frame.

[0061] TOF counter 506 is operable to maintain a running count of clock cycles on master clock 414. TOF counter 506 is reset at the start of each detection frame via master clock enable 416.

[0062] TOF register module 508 includes a plurality of TOF registers and control circuitry for storing the count of TOF counter 506 in a different TOF register each time a reflection 112 is detected at GmAPD 502 during a detection frame, thereby enabling registration of the time-of-flight information of each of the multiple reflections 112 received at GmAPD 502 during a single detection frame. TOF register module 508 provides the stored TOF data of each reflection 112 detected during a single detection to processor 306 via data output signal 516.

[0063] The ability to detect multiple reflections received at a pixel during a single detection frame and store the 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 herein. It should be noted that the embodiments and methods described herein merely illustrate some of the methods within the scope of the present disclosure, and numerous alternative systems and methods are within that scope.

[0064] Figure 6 Operation of a method for interrogating a detection region according to the present disclosure is depicted. Method 600 begins at operation 601, where transmitter 102 emits output signal 108 towards detection region 114. As in system 100 described above, in the depicted example, output signal 108 comprises a periodic sequence of n optical pulses (i.e., optical pulses 110-1 to 110-n) exhibiting period T1. Reference is continued herein Figures 3 to 5 and Figures 7 to 10 to describe method 600.

[0065] 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 detection region 114 within each detection frame 802(i). It should be noted that detection frames 802(1) to 802(n) together define an image frame similar to image frame 202.

[0066] Figure 7 Sub-operations of an exemplary sub-method suitable for enabling a pixel to detect multiple reflections during a single detection frame according to the present disclosure are depicted.

[0067] Figure 8 A timing diagram of a representative detection frame for one pixel 404 according to sub-method 700 is depicted.

[0068] 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 optical 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.

[0069] In sub-operation 702, at time t1, the processor 306 provides an electrical pulse on the global activation 410 to the strobe signal controller 504. In response, the strobe signal controller provides an electrical pulse on the strobe signal 512, which activates the GmAPD 502 to place it in Geiger mode. In the depicted example, as described above, time t1 is similar to the activation time ta; thus, the GmAPD 502 is activated substantially at the same time as each optical pulse 110 is emitted. However, it should be noted that these actions can be performed at different times. It should be noted that the global activation 410 is also a global signal provided to each pixel 404 of the detector 308.

[0070] The generation of the electrical pulse on the global activation 410 defines the start of a range gate 804 during which the GmAPD 502 can be operable for detecting the reflection 112.

[0071] In sub-operation 703, as Figure 8 seen, at time tr-1, the first reflection 112-1 is received at the GmAPD 502. Receiving the reflection 112-1 causes an avalanche detection event, which results in an electrical pulse on the APD signal 510. Those skilled in the art will recognize that the reflection can be received at the GmAPD 502 at any time within the detection frame 802(i).

[0072] The APD signal 510 is directed to the strobe signal controller 504, the TOF counter 506, and the TOF register module 508.

[0073] In sub-operation 704, in response to the electrical pulse on the APD signal 510, the value of the TOF counter 506 at time tr-1 is captured and stored in the first TOF register in the TOF register module 508 as the TOF data 514-1. The TOF data 514-1 serves as the TOF timestamp for the reflection 112-1.

[0074] In sub-operation 705, in response to an 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 during the hold-off time 806, the duration of which is defined by the global hold-off 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 the 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, and in a manner similar to the above-described hold-off time 208 and with respect to the system 100, the duration of the hold-off time 806 is selected to mitigate false counts due to follow-up pulses of the GmAPD 502.

[0075] In sub-operation 706, the strobe signal controller 504 reactivates the GmAPD 502 at the end of the hold-off time 806 (i.e., at time t3) by increasing the level of the strobe signal 512 above the threshold Vt of the GmAPD.

[0076] Then, the functional sequence of sub-operations 703 to 706 is 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 strobe period 804.

[0077] For example, as Figure 8 depicted, at any 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. Then, the GmAPD 502 is quenched again at time t4 and reactivated at time t5 after the hold-off time 806.

[0078] In the depicted example, during the detection frame 802(i), only two reflections 112 (i.e., m = 2) are detected at the pixel 404. However, those skilled in the art should be clear that, without departing from the scope of the present disclosure, m can have any value from 0 to n. In fact, the value of m is only limited by the number of TOF registers included in the TOF register module 508, the duration of the range strobe 804, and the length of the hold-off time 806 required to mitigate false counts due to follow-up pulses in the GmAPD 502. In the depicted example, n = 3, the range strobe 804 is approximately 2 microseconds, and the hold-off time 806 is approximately 0.5 microseconds.

[0079] In sub-operation 707, the processor 306 provides a global deactivation 412 to the strobe signal controller 504 at time t6, which defines the end of the range strobe 804. In response, the strobe signal controller deactivates the GmAPD 502 by reducing the strobe signal 512 below the threshold voltage Vt. Typically, time t6 is slightly earlier than the end of the detection frame 802(i), thereby establishing a hold-off time 808 for all pixels 404 of the pixel array. Similar to the hold time 208 described above, the hold-off time 808 allows trapped charges in the GmAPD to be detrapped and recombined before the start of the next detection frame, thereby advantageously avoiding spurious avalanche events such as dark counts due to follow-on pulses.

[0080] After the global deactivation 412 becomes effective, any ongoing hold-off time 806 terminates.

[0081] 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 start of each range strobe 804 and synchronously deactivated at the end of each range strobe 804 via the global activation 410 and the global deactivation 412, respectively. However, including the strobe signal controller 504 within each pixel enables each pixel to be deactivated, quenched, and reactivated several times within the 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.

[0082] Now returning to method 600, in operation 603, the TOF data 514-1 to 514-m is read out to the processor 306 as data output 516. Typically, the TOF data is read out in response to the global deactivation 412 becoming effective at time t6.

[0083] In operation 604, the processor 306 calculates the range of any object 116 identified in the detection region 114, where the range of such object is estimated based on the data output signals 516 received from each pixel 404.

[0084] Figure 9 An exemplary circuit arrangement of a strobe signal controller in accordance with the present disclosure is depicted. The strobe signal controller 504 includes a hold-off timer 902, an activation timer 904, a bias controller 906, and conventional summing nodes 908-1 and 908-2.

[0085] The blanking 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 blanking timer 902 holds the blanking signal 910 low during a blanking period based on the global blanking time 420. The global blanking time 420 is typically received from the processor 306 or stored in a configuration register included in the ROIC 310. The blanking timer 902 is included in the pixel 404 to keep the GmAPD 502 deactivated for a period of time after an avalanche detection event to allow the trapped charge in its active region to recombine before the GmAPD is reactivated. Thus, including the blanking timer 902 reduces false alarms generated in the system 300 due to follow-on pulses in one or more of the pixels 404.

[0086] 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 enables the activation signal 912 when the blanking period of the blanking timer 902 expires or when the global activation 410 becomes effective, receiving a combination of the expiration of the blanking period at the blanking timer 902 or the effectiveness of the global activation 410 from the summing node 908-1. 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.

[0087] 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 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 effectiveness of one or both of these signals causes the deactivation signal 914 to become effective.

[0088] The bias controller 906 activates the GmAPD 502 in response to the effectiveness of the activation signal 912 and deactivates the GmAPD in response to the effectiveness of the deactivation signal 914.

[0089] The strobe signal controller 504 is configured to deactivate the GmAPD 502 in response to either (1) the effectuation 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 hold-off timer 902 initiates a hold-off time 806 to ensure that the avalanche detection event initiated by the absorption of the reflection is fully quenched and that substantially all of the trapped charge becomes released before the GmAPD is reactivated. Alternatively, in response to the global deactivation 412, the hold-off timer does not initiate a hold-off time, but directly quenches the application to the GmAPD during the duration of the global deactivation signal. This is typically applied at the end of a range strobe sequence to deactivate all of the GmAPDs of the pixel array 402 at the end of the detection frame 802.

[0090] The strobe signal controller 504 is further configured to place the GmAPD 502 in Geiger mode in response to either (1) the effectuation of the global activation 410 or (2) automatically after the expiration of the hold-off period of the hold-off timer 902.

[0091] It should be noted that, as Figure 9 depicted, the strobe signal controller 504 is merely one example of a suitable configuration within the scope of the present disclosure.

[0092] Figure 10 A functional block diagram of a TOF register module in accordance with an illustrative embodiment is depicted. The TOF register module 508 includes TOF register banks 1002A and 1002B, a controller 1004, and a serial output multiplexer 1006.

[0093] Each of the TOF register banks 1002A and 1002B (hereinafter referred to as banks 1002A and 1002B) includes substantially identical TOF registers 1008-1 to 1008-n (collectively referred to as TOF registers 1008).

[0094] Banks 1002A and 1002B are operatively coupled to the controller 1004 such that the TOF data for the current detection frame can be read into one of banks 1002A and 1002B while the other bank holds the TOF data from the previous detection frame.

[0095] Banks 1002A and 1002B are also operatively coupled to the serial output multiplexer 1006, which enables the TOF data stored in their registers to be serially read out to the processor 306 as data output 516.

[0096] The controller 1004 is a circuit controller for receiving TOF data 514 from the TOF counter 506 and storing the TOF data in one of the TOF register banks 1002A and 1002B. The controller 1004 is configured to exchange the functions of the banks 1002A and 1002B between capture and readout, thereby enabling the "integrate-on-read" capability. In other words, the TOF register module 508 can read out TOF data from a previous detection frame while TOF data of the current detection frame is being stored. The capture and readout functions of the banks 1002A and 1002B are controlled by the bank selection signal 1010.

[0097] The serial output multiplexer 1006 is a conventional serial peripheral interface (SPI) and, as determined by the bank selection signal 1010 from the controller 1004, the serial output multiplexer 1006 is operable to serially read out TOF data stored in the TOF register 1008 of one of the banks 1002A and 1002B.

[0098] It should be noted that, as Figure 10 depicted, the TOF register module 508 is only one example of a suitable configuration of the TOF register module within the scope of the present disclosure. For example, in some embodiments, only one TOF register bank is included in the TOF register module 508. In some embodiments, more than two TOF register banks are included in the TOF register module 508.

[0099] It is to be understood that the present disclosure only teaches some examples of embodiments of the present invention, and after reading the present disclosure, those skilled in the art can easily envision many variations of the present invention, and the scope of the present 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 periodic light pulses towards a detection area; and a receiver including a plurality of pixels, wherein a pixel among the plurality of pixels is configured to detect multiple reflections of a light pulse in the series of periodic light pulses during a detection frame among a plurality of detection frames, the detection frame having a duration based on a period of the series of periodic light pulses and having a start time based on an emission of another light pulse in the series of periodic light pulses, wherein each pixel includes: a Geiger mode avalanche photodiode GmAPD configured to: generate an APD signal in response to each of the multiple reflections being detected during the detection frame, be activated to be in Geiger mode in response to a gating signal being in an active state, and be deactivated to exit the Geiger mode in response to the gating signal being in a non-active state; a gating signal controller including a summing node configured to combine the APD signal and a global deactivation signal as a deactivation signal, wherein the global deactivation signal is received by each of the plurality of pixels; a time-of-flight TOF counter for tracking a time between an emission of the light pulse and a detection of the multiple reflections of the light pulse; and a TOF register module for storing TOF data associated with the multiple reflections of the light pulse.

2. The LiDAR system according to claim 1, further comprising a processor configured to form a detection area map based on the TOF data stored in the TOF register module of at least one pixel among the plurality of pixels.

3. The LiDAR system according to claim 1, further comprising a processor configured to provide at least one global signal to each 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 LiDAR system according to claim 1, wherein, the gating signal controller is configured to deactivate the GmAPD in response to a detection of the multiple reflections or in response to the global deactivation signal being received by each of the plurality of pixels.

5. The LiDAR system according to claim 1, wherein, the gating signal controller includes: a blanking timer configured to generate a blanking signal in response to an activation of an APD signal from the GmAPD; an activation timer configured to activate an activation signal in response to an activation of the blanking signal and a global activation signal, wherein the global activation signal is received at each of the plurality of pixels; and a bias controller configured to provide the gating signal, wherein the bias controller provides a gating signal in an active state in response to an activation of the activation signal and provides a gating signal in a non-active state in response to an activation of the deactivation signal.

6. A method for estimating a range of at least one object in a detection area, the method comprising: Emit a series of periodic light pulses towards the detection region; Define a plurality of detection frames, wherein each detection frame of the plurality of detection frames has a duration based on the period of the series of periodic light pulses and has a start time based on the emission of a corresponding one of the series of periodic light pulses; Receive a first reflection of a first light pulse of the series of periodic light pulses at a first pixel of a receiver during a first detection frame of the plurality of detection frames, wherein the first pixel includes a first Geiger mode avalanche photodiode GmAPD, and wherein a first avalanche detection event is triggered in the GmAPD in response to receiving the first reflection; Asynchronously deactivate the first GmAPD to quench the first avalanche detection event; Asynchronously activate the first GmAPD to initiate a second avalanche detection event in response to receiving a second reflection of the first light pulse of the series of periodic light pulses during the first detection frame; and Deactivate the first GmAPD and a second GmAPD included in a second pixel of the receiver, wherein the first GmAPD and the second GmAPD are deactivated synchronously at a first time, the first time being based on the start time of a second detection frame of the plurality of detection frames.

7. The method according to claim 6, further comprising synchronously activating the first GmAPD and the second GmAPD at a second time, the second time being based on the start time of the second detection frame.

8. The method according to claim 6, further comprising tracking the time between the emission of the first light pulse and the reception of the first reflection.

9. The method according to claim 6, further comprising: Store a first time-of-flight TOF value in a first TOF register, the first TOF value being based on a first delay between the emission of the first light pulse and the reception of the first reflection at the first GmAPD; and Store a second TOF value in a second TOF register, the second TOF value being based on a second delay between the emission of the first light pulse and the reception of a second reflection of the first light pulse at the first GmAPD during the first detection frame.

10. The method according to claim 9, further comprising: Store a third TOF value in a third TOF register, the third TOF value being based on a third delay between the emission of a second light pulse of the series of periodic light pulses and the reception of a third reflection of the second light pulse at the first GmAPD during a second detection frame of the plurality of detection frames; Store a fourth TOF value in a fourth TOF register, the fourth TOF value being based on a fourth delay between the emission of the second light pulse and the reception of a fourth reflection of the second light pulse at the first GmAPD during the second detection frame; and While the third TOF value and the fourth TOF value are stored, provide the first TOF value and the second TOF value to a processor.

11. A light detection and ranging LiDAR system, comprising: a light source for emitting a series of periodic light pulses towards a detection area; a receiver including a plurality of pixels, wherein each pixel of the plurality of pixels is configured to detect multiple reflections of the light pulses in the series of periodic light pulses during a detection frame among a plurality of detection frames, wherein each pixel includes: a Geiger mode avalanche photodiode GmAPD configured to generate an APD signal in response to each of the multiple reflections being detected during the detection frame; a gating signal controller configured to asynchronously activate and asynchronously deactivate the GmAPD, and including a summing node configured to combine the APD signal and a global deactivation signal as a deactivation signal, wherein the global deactivation signal is received by each pixel of the plurality of pixels; a counter for determining a delay between the emission of the light pulse and the reception of each of the multiple reflections of the light pulse; and a plurality of time-of-flight TOF registers for storing TOF data corresponding to each of the multiple reflections.

12. The LiDAR system according to claim 11, further comprising a processor configured to form a detection area map based on the TOF data stored in the TOF registers of at least one pixel of the plurality of pixels.

13. The LiDAR system according to claim 11, wherein, the receiver is configured such that the GmAPDs of the plurality of pixels can be synchronously activated at a first time based on the start time of each of the plurality of detection frames.

14. The LiDAR system according to claim 13, wherein, the receiver is configured such that the GmAPDs of the plurality of pixels can be synchronously deactivated at a second time based on the emission of another light pulse in the series of periodic light pulses.

15. The LiDAR system according to claim 11, further comprising a processor further configured to provide at least one global signal to each pixel 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.

16. The LiDAR system according to claim 11, wherein, the gating signal controller includes a hold-off timer configured to generate a hold-off signal in response to the APD signal becoming valid.

17. The LiDAR system according to claim 11, wherein, the gating signal controller includes an activation timer configured to make an activation signal become valid in response to the hold-off signal and the global activation signal becoming valid, wherein the global activation signal is received by each pixel of the plurality of pixels.

18. The LiDAR system according to claim 11, wherein, The gating signal controller further includes another summing node configured to combine an APD signal from the GmAPD and a global activation signal to output an activation signal, where the global activation signal is received by each of the plurality of pixels.

19. A time-of-flight (TOF) register module, comprising: a first TOF register bank configured to store TOF data for a current detection frame; a second TOF register bank configured to store TOF data from a previous detection frame; a controller configured to: receive TOF data from a TOF counter, store the TOF data in one of the first TOF register bank and the second TOF register bank, and exchange the functions of the first TOF register bank and the second TOF register bank between capture and readout to enable read integration capability; and a serial output multiplexer configured to: read out TOF data in one of the first TOF register bank and the second TOF register bank, and serially output the TOF data based on a bank selection signal received from the controller.

20. The TOF register module according to claim 19, wherein the function between capture and readout is controlled by the bank selection signal, and wherein the serial output multiplexer is further configured to read out TOF data from the previous detection frame while the TOF data of the current detection frame is being stored.

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