LiDAR SYSTEM WITH ACTIVE FAULT MONITORING

Abstract

To provide a LiDAR system with active fault monitoring.SOLUTION: A method for detecting a fault condition in a light detection and ranging transmitter includes generating a control signal that comprises an address and desired drive voltage and current information for a laser in a laser array. A drive signal is generated for the laser in the laser array in response to the generated control signal, and applied to a contact associated with the address of the laser array, thereby energizing the laser at a desired output power for a desired time. A determination is made on whether the drive signal has a parameter with a value that is outside a threshold range for eye safety. The address and the fault condition are stored if the parameter has the value outside the threshold range for eye safety, and reported to a host that takes an action on the LiDAR transmitter in response to the fault condition.SELECTED DRAWING: None

Description

[Background technology]

[0001] The section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described in the present application in any way.

[0002] (Related Application Section) This application is a non-provisional application of U.S. Provisional Patent Application No. 63 / 158,739, entitled “LiDAR System with Active Fault Monitoring,” filed March 9, 2021. The entire contents of U.S. Provisional Patent Application No. 63 / 158,739 are incorporated herein by reference.

[0003] (Introduction) Autonomous, self-driving, and semi-autonomous vehicles use a combination of different sensors and technologies, such as radar, image recognition cameras, and sonar, for detection and location of surrounding objects. These sensors enable numerous improvements in driver safety, including collision warning, automatic emergency braking, lane departure warning, lane keeping assist, adaptive cruise control, and piloted driving. Among these sensor technologies, Light Detection and Ranging (LiDAR) systems play a key role, enabling real-time, high-resolution 3D mapping of the surrounding environment.

[0004] Today, modern LiDAR systems used for autonomous vehicles utilize a small number of lasers combined with some method of mechanically scanning the environment. Some state-of-the-art LiDAR systems use two-dimensional vertical cavity surface emitting laser (VCSEL) arrays as illumination sources and various types of solid-state detector arrays in the receiver. It is highly desirable for future autonomous automobiles to utilize solid-state semiconductor-based LiDAR systems with high reliability and wide environmental operating range. These solid-state LiDAR systems are advantageous because they use solid-state technology with no moving parts. However, current state-of-the-art LiDAR systems have many practical limitations, and new systems and methods are needed to improve performance, safety, reliability, and user experience. Summary of the Invention [Means for solving the problem]

[0005] The present teachings will now be described in more detail with reference to exemplary embodiments thereof as illustrated in the accompanying drawings. While the present teachings will be described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. Rather, the present teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those skilled in the art. Those skilled in the art with access to the teachings herein will recognize additional implementations, modifications, and embodiments that are within the scope of the present disclosure as described herein, and other fields of use.

[0006] Reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the present teachings. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

[0007] It should be understood that the individual steps of the methods of the present teachings may be performed in any order and / or simultaneously so long as the present teachings remain operable. Further, it should be understood that the apparatus and methods of the present teachings may include any number or all of the described embodiments so long as the present teachings remain operable.

[0008] The present teachings generally relate to Light Detection and Ranging (LiDAR), a remote sensing method that uses laser light to measure distance (range) to objects. LiDAR systems generally measure distance to various objects or targets that reflect and / or scatter light. Autonomous vehicles use LiDAR systems to generate highly accurate 3D maps of the surrounding environment with high resolution. The systems and methods described herein are directed to providing a solid-state pulsed time-of-flight (TOF) LiDAR system with a high level of reliability while also maintaining a long measurement range and low cost.

[0009] The present teachings describe various embodiments of LiDAR systems that can monitor and detect faults affecting transmitter operation and take action based on the fault condition, providing improved safety, reliability, and usability of the system. The described systems and methods provide improved monitoring of faults in LiDAR systems, as well as methods and algorithms for adapting to those faults. These features provide significant improvements in system safety and product operation. The present invention provides, for example, the following: (Item 1) 1. A method for detecting a fault condition in a Light Detection and Ranging (LiDAR) transmitter, the method comprising: a) generating control signals containing addresses and desired drive voltages and currents for the lasers in the laser array; b) generating, in response to the generated control signals, drive signals for the lasers in the laser array and applying the generated drive signals to contacts of the laser array associated with that address, thereby energizing the lasers at a desired output power for a desired time; c) determining whether the drive signal has a parameter with a value that is outside a threshold range for eye safety; and d) storing the address and a fault condition if the parameter has the value outside the eye-safety threshold range; e) reporting the address and the fault condition to a host that takes action on the LiDAR transmitter in response to the fault condition; A method comprising: (Item 2) Item 2. The method of item 1, wherein the laser comprises a group of lasers in the laser array. (Item 3) 2. The method of claim 1, wherein the parameter comprises a drive signal pulse duration. (Item 4) 2. The method of claim 1, wherein the parameter includes a drive signal power. (Item 5) 2. The method of claim 1, wherein the parameter comprises a drive signal repetition rate. (Item 6) Item 10. The method of item 1, wherein the drive signal includes a low side drive signal. (Item 7) Item 10. The method of item 1, wherein the drive signal includes a high side drive signal. (Item 8) 2. The method of claim 1, wherein determining whether the drive signal has a parameter with a value that is outside a threshold range for eye safety includes performing an XOR operation. (Item 9) 2. The method of claim 1, wherein determining whether the drive signal has a parameter with a value that is outside a threshold range for eye safety includes comparing the drive current to a predetermined low current value. (Item 10) 2. The method of claim 1, wherein determining whether the drive signal has a parameter with a value that is outside a threshold range for eye safety includes comparing the drive voltage to a predetermined low voltage value. (Item 11) 2. The method of claim 1, wherein determining whether the drive signal has a parameter with a value that is outside a threshold range for eye safety includes comparing the drive voltage to a predetermined high voltage value. (Item 12) 2. The method of claim 1, wherein determining whether the drive signal has a parameter with a value that is outside a threshold range for eye safety includes comparing the drive current to a predetermined high current value. (Item 13) 2. The method of claim 1, wherein determining whether the drive signal has a parameter with a value that is outside a threshold range for eye safety includes comparing the drive current to a predetermined low current value. (Item 14) 2. The method of claim 1, wherein determining whether the drive signal has a parameter with a value that is outside a threshold range for eye safety includes comparing the drive voltage to a predetermined low voltage value. (Item 15) 2. The method of claim 1, wherein determining whether the drive signal has a parameter with a value that is outside a threshold range for eye safety includes comparing the drive voltage to a predetermined high voltage value. (Item 16) 2. The method of claim 1, wherein determining whether the drive signal has a parameter with a value that is outside a threshold range for eye safety includes comparing the drive current to a predetermined high current value. (Item 17) 2. The method of claim 1, wherein the drive voltage is a high side drive voltage. (Item 18) 2. The method of claim 1, wherein the drive voltage is a low side drive voltage. (Item 19) Item 10. The method of item 1, wherein the laser array comprises a two-dimensional laser array. (Item 20) 20. The method of claim 19, wherein the laser array has at least two lasers that can be operated independently. (Item 21) 2. The method of claim 1, further comprising reporting the severity of the fault condition to the host. (Item 22) 2. The method of claim 1, further comprising performing additional diagnostics in response to the fault condition. (Item 23) 2. The method of claim 1, wherein the host adapts operating parameters based on the fault condition. (Item 24) 2. The method of claim 1, wherein the host alters a firing sequence based on the fault condition. (Item 25) 2. The method of claim 1, wherein the host alters laser-to-pixel mapping based on the fault condition. (Item 26) 2. The method of claim 1, further comprising reporting a health status to a host that takes action on the LiDAR transmitter in response to the health status. (Item 27) 1. A method for detecting a fault condition in a Light Detection and Ranging (LiDAR) transmitter, the method comprising: a) generating control signals including addresses and desired drive voltage information for lasers in a laser array; b) generating, in response to the generated control signals, drive signals for the lasers in the laser array and applying the generated drive signals to contacts of the laser array associated with that address, thereby energizing the lasers at a desired output power for a desired time; c) determining whether the drive signal has a parameter with a value that is outside a threshold range for functional safety; d) if the parameter has the value outside a threshold range for the functional safety, storing the address and a fault condition; e) reporting the address and the fault condition to a host that takes action on the LiDAR transmitter in response to the fault condition; A method comprising: (Item 28) 28. The method of claim 27, wherein determining whether the drive signal has a parameter with a value that is outside a threshold range for functional safety includes comparing a drive current to a predetermined low current value. (Item 29) 28. The method of claim 27, wherein determining whether the drive signal has a parameter with a value that is outside a threshold range for functional safety comprises comparing the drive voltage to a predetermined low voltage value. (Item 30) 28. The method of claim 27, wherein determining whether the drive signal has a parameter with a value that is outside a threshold range for functional safety includes comparing the drive voltage to a predetermined high voltage value. (Item 31) 28. The method of claim 27, wherein determining whether the drive signal has a parameter with a value that is outside a threshold range for functional safety includes comparing a drive current to a predetermined high current value. (Item 32) 28. The method of claim 27, wherein the drive voltage is a high side drive voltage. (Item 33) 28. The method of claim 27, wherein the drive voltage is a low side drive voltage. (Item 34) 28. The method of claim 27, wherein the laser array comprises a two-dimensional laser array. (Item 35) Item 35. The method of item 34, wherein the laser array has at least two lasers that can be operated independently. (Item 36) 28. The method of claim 27, further comprising reporting the severity of the fault condition to the host. (Item 37) 30. The method of claim 27, further comprising performing additional diagnostics in response to the fault condition. (Item 38) 28. The method of claim 27, wherein the host adapts operating parameters based on the fault condition. (Item 39) 28. The method of claim 27, wherein the host alters the firing sequence based on the fault condition. (Item 40) 28. The method of claim 27, wherein the host alters the laser-to-pixel mapping based on the fault condition. (Item 41) 28. The method of claim 27, further comprising reporting a health status to a host that takes action on the LiDAR transmitter in response to the health status. (Item 42) 1. A method for detecting a health condition in a Light Detection and Ranging (LiDAR) transmitter, the method comprising: a) generating control signals including addresses and desired drive voltage information for lasers in a laser array; b) determining a value related to a health condition of the lasers in the laser array; and c) storing the address and the value of the health condition if the value is outside a threshold range for functional safety; d) reporting the address and the fault condition to a host that takes action on the LiDAR transmitter in response to the health condition; A method comprising: [Brief description of the drawings]

[0010] In accordance with preferred exemplary embodiments, the present teachings, together with further advantages thereof, are more particularly described in the following detailed description taken in conjunction with the accompanying drawings. Those skilled in the art will appreciate that the drawings described below are for illustrative purposes only. The drawings are not necessarily to scale, with emphasis instead generally being placed upon illustrating the principles of the present teachings. The drawings are not intended to limit the scope of applicant's teachings in any way.

[0011] [Figure 1] FIG. 1 illustrates one embodiment of a LiDAR system of the present teachings implemented in a vehicle.

[0012] [Figure 2A] FIG. 2A illustrates a block diagram of one embodiment of a monitored system including a LiDAR transmitter and receiver system connected to a host processor of the present teachings.

[0013] [Figure 2B]FIG. 2B illustrates a block diagram of one embodiment of a monitored LiDAR transmitter and receiver system with a transmission subassembly for illuminating a target of the present teachings.

[0014] [Figure 2C] FIG. 2C illustrates an expanded view of the transmission subassembly of FIG. 2B.

[0015] [Figure 2D] FIG. 2D illustrates a close-up view of a high-side current pulse embodiment of the transmission subassembly of the present teachings.

[0016] [Figure 2E] FIG. 2E illustrates a close-up view of a low-side current pulse embodiment of the transmission subassembly of the present teachings.

[0017] [Figure 2F] FIG. 2F illustrates an example failure mode for light output as a function of time related to eye safety for an embodiment of a monitored LiDAR transmitter of the present teachings.

[0018] [Diagram 3] FIG. 3 illustrates one embodiment of the transmission electronics of the LiDAR transmitting and receiving system of FIG. 2A.

[0019] [Figure 4] FIG. 4 illustrates one embodiment of a diagnostic module for the transmission electronics embodiment of FIG.

[0020] [Figure 5A] FIG. 5A illustrates one embodiment of a transmission subassembly for a VCSEL array in relation to a monitored LiDAR transmitter of the present teachings.

[0021] [Figure 5B]FIG. 5B illustrates one embodiment of a VCSEL array transmit subassembly for a monitored LiDAR transmitter with shared diagnostic circuitry for the low-side and high-side drivers of the present teachings.

[0022] [Figure 5C] FIG. 5C illustrates one embodiment of a transmit subassembly for a VCSEL array for a monitored LiDAR transmitter with separate diagnostic circuitry for the low-side and high-side drivers of the present teachings.

[0023] [Figure 6] FIG. 6 illustrates a table showing an example embodiment of fault criteria, faults, and controller responses for idle operation for a monitored LiDAR system of the present teachings.

[0024] [Figure 7] FIG. 7 illustrates a table showing an example embodiment of fault criteria, faults, and controller responses for active operation in high side drive for a monitored LiDAR system of the present teachings.

[0025] [Figure 8A] FIG. 8A illustrates a graph showing the time dependence of good active and inactive channels and high thresholds at the anode for a monitored LiDAR system of the present teachings.

[0026] [Figure 8B] FIG. 8B illustrates a graph showing the time dependence of poor active and inactive channels and high thresholds at the anode for a monitored LiDAR system of the present teachings.

[0027] [Figure 9] FIG. 9 illustrates a table showing an example embodiment of fault criteria, faults, and controller responses with respect to low voltage thresholds at the anode for a monitored LiDAR system of the present teachings.

[0028] [Figure 10A] FIG. 10A illustrates a graph showing good active and inactive channels and time dependence of thresholds at anode at low voltage threshold for a monitored LiDAR system of the present teachings.

[0029] [Figure 10B] FIG. 10B illustrates a graph showing time dependence of bad inactive channels and threshold at low voltage threshold at the anode for a monitored LiDAR system of the present teachings.

[0030] [Figure 11] FIG. 11 illustrates a table showing an example embodiment of fault criteria, faults, and controller responses for active channels at the cathode at low voltage thresholds for a monitored LiDAR system of the present teachings.

[0031] [Figure 12A] FIG. 12A illustrates a graph showing good active and inactive channels and time dependence of threshold at the cathode at low voltage threshold for a monitored LiDAR system of the present teachings.

[0032] [Figure 12B] FIG. 12B illustrates a graph showing the time dependence of poor active and inactive channels and thresholds at the cathode at low voltage thresholds for a monitored LiDAR system of the present teachings.

[0033] [Figure 13] FIG. 13 illustrates a table showing an example embodiment of fault criteria, faults, and controller responses for active channels at a high voltage threshold for the cathode for a monitored LiDAR system of the present teachings.

[0034] [Figure 14A] FIG. 14A illustrates a graph showing good active and inactive channels and the time dependence of thresholds at the cathode at high voltage threshold for a monitored LiDAR system of the present teachings.

[0035] [Figure 14B] FIG. 14B illustrates a graph showing time dependence of bad inactive channels and threshold at the cathode at high voltage threshold for a monitored LiDAR system of the present teachings.

[0036] [Figure 15] FIG. 15 illustrates a table showing an example embodiment of faults and controller responses related to monitored pulse widths for a monitored LiDAR system of the present teachings.

[0037] [Figure 16] FIG. 16 illustrates a graph showing the time dependence of pulses in the high side drive at the anode for a monitored LiDAR system of the present teachings.

[0038] [Figure 17] FIG. 17 illustrates a timing diagram for high side drive and low side drive and light pulses of one embodiment of a monitored LiDAR system of the present teachings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] 1 illustrates a LiDAR system 100 of the present teachings implemented within a vehicle. The LiDAR system 100 includes a laser projector 101, also referred to as an illuminator, that projects a light beam 102 generated by a light source toward a target scene, and a receiver that receives light 104 reflected from an object, shown as a person 106, in the target scene. In some embodiments, the illuminator includes a laser transmitter and various delivery optics.

[0040] A LiDAR system typically also includes a controller that calculates distance information about an object 106, shown in the figure as a person, from the reflected light. In some embodiments, there are also elements that can scan or otherwise provide a specific pattern of light, which can be a static or dynamic pattern across a desired range and field of view (FOV). A portion of the reflected light from the object 106 is received by a receiver. In some embodiments, the receiver comprises receiving optics and a detector element, which can be an array of detectors. The receiver and controller are used to convert the received signal light into measurements that represent a point-by-point 3D map of the surrounding environment within the range and FOV of the LiDAR system.

[0041] Some embodiments of the LiDAR system according to the present teachings use a laser transmitter that is a laser array. In some specific embodiments, the laser array comprises VCSEL laser devices. These may include top-emitting VCSELs, bottom-emitting VCSELs, external cavity VCSELs, and various types of high-power VCSELs. The VCSEL array may be monolithic. The laser emitters may all share a common substrate, including a semiconductor substrate or a ceramic substrate.

[0042] In some embodiments, individual lasers and / or groups of lasers in embodiments using one or more transmitter arrays can be individually controlled. Each individual emitter in a transmitter array can be fired independently, with the optical beam emitted by each laser emitter corresponding to a 3D projection angle for only a portion of the total system field of view. One example of such a LiDAR system is described in U.S. Patent Publication No. 2017 / 0307736A1 (assigned to the present assignee). The entire contents of U.S. Patent Publication No. 2017 / 0307736A1 are incorporated herein by reference. In addition, the number of pulses fired by individual lasers or groups of lasers can be controlled based on the desired performance objectives of the LiDAR system. The duration and timing of this sequence can also be controlled to achieve various performance goals.

[0043] One feature of the present teachings is to provide a monitored LiDAR system that can detect faults affecting transmitter operation and, in some circumstances, take corrective action based on these fault conditions, providing improved safety, reliability, and usability of the LiDAR alone or within a larger sensor system of which the LiDAR is a part. In some sensor systems, the LiDAR is connected to a host processor that manages higher level sensor functions and system actions and responses. In some sensor systems, the LiDAR is connected to a host processor that manages the LiDAR sensor as a standalone sensor system. One feature of the present teachings is that it provides a monitoring capability that can be located in the vicinity of the transmission assembly and / or subassembly hardware, and thus is able to monitor, identify, and / or respond to fault conditions at the contact points in proximity to the laser device that generates the light emitted in the transmitter. This approach provides numerous advantages. For example, response times can be quicker and / or the cost and complexity of components required to find and react to faults can be reduced. Fault identification can be rapid and / or preemptive. Reactions to faults can occur during operation. Actions in response to faults can be taken on parts of the system while allowing other parts of the system to continue operation, for example resulting in gradual degradation rather than sudden failure. Using local processing, the decision to transmit and / or escalate a reaction to a fault to a higher level operating system can reduce the burden on the operating system and improve system reliability overall. The above are merely examples of benefits of the monitored LiDAR transmitter systems and methods of the present teachings.

[0044] One feature of the monitored LiDAR systems of the present teachings is that they can provide synthesized fault information to the host system so that the host system can respond and react in an efficient and effective manner. FIG. 2A illustrates a block diagram of an embodiment of a monitored system 200 including a LiDAR transmitter and receiver system 201 connected to a host processor 214 of the present teachings. The LiDAR transmitter and receiver system (LiDAR system) 201 connected to the host processor 214 has six main components: (1) controller and interface electronics 202, (2) transmission electronics 204 including laser drivers, (3) laser array 206, (4) receiving and time-of-flight and intensity calculation electronics 208, (5) detector array 210, and (6) in some embodiments, an optical monitor 212. The LiDAR system controller and interface electronics 202 controls the overall function of the LiDAR system 201 and provides digital communication to the host system processor 214. The transmission electronics 204 controls the operation of the laser array 206 and, in some embodiments, sets the pattern and / or power of the laser firing of the individual elements in the array 206. The receiving and time-of-flight calculation electronics 208 receives the electrical detection signals from the detector array 210 and then processes these electrical detection signals to calculate the range distance through time-of-flight calculations. The strength of the return signal is also calculated in the electronics 208.

[0045] Optional temperature sensors 205, 209 may also be used for control and operation of the transmitter and / or receiver. A transmit temperature sensor 205 may be placed in proximity to the laser array 206. The transmit temperature sensor 205 output is electrically connected to the transmit electronics 204. A receive temperature sensor 209 may be placed in proximity to the detector array 210 with the output electrically connected to the receive electronics 208. The temperature sensors 205, 209 may provide various thermal monitoring to the electronics 204, 208 and other controllers (connections not shown) in the monitored system 200. For example, a fault condition in the laser array 206 may cause excessive power dissipation that would result in a temperature difference between the system temperature sensor (not shown) and the laser array temperature sensor 205, which is typically positioned some distance away from the array. Identification of this thermal gradient may cause the transmit controller 204 to stop firing the lasers in the array 206. For example, over-temperature or under-temperature conditions of the various laser arrays 206 identified using temperature sensors 205 will cause the transmit controller 204 to pause firing. These conditions may be absolute temperature conditions or they may be conditions based on other temperature conditions internal and / or external to the system 200. Similar identification of and reaction to over-temperature and / or under-temperature functions is provided for the detector array 210 using receiver temperature sensors 209.

[0046] In some embodiments, the transmission controller 204 reduces the light output by reducing the pulse current and / or by reducing the pulse duty cycle to overcome moderate over-temperature conditions. In some embodiments, the transmission controller 204 controls pulse parameters such as pulse amplitude, pulse width, and / or pulse delay. In some embodiments, the transmission controller 204 will adjust the pulse amplitude, pulse width, and / or pulse delay to compensate for the thermal dependency of the driver. Also, in some embodiments, the transmission controller 204 will adjust the pulse amplitude, pulse width, and / or pulse delay to compensate for the temperature dependency of the laser array 206. For example, during a cold start, the transmission controller 204 can drive the laser array 206 to perform laser firing and heat up the system, which can be managed by input from the temperature sensor 205. In some embodiments, the transmission controller 204 can capture data from the temperature sensor 205 and find a temperature change large enough to cause a thermal shock, which may cause cracks or other failures in the optical and / or electronic components in the system 201.

[0047] 2B illustrates a schematic diagram of a sensor system 220 including an embodiment of a monitored LiDAR transmitter and receiver system 221 with a transmission subassembly 222 illuminating a target 224 of the present teachings. In this example, the target 224 is a bicycle with a rider, which serves to emphasize the importance of the eye safety requirements of the monitored LiDAR transmitter and receiver system 221. The LiDAR transmitter and receiver system 221 has a transmission assembly 226 and a receiver assembly 228, which are connected to a LiDAR system control processor 225. An expanded block diagram of the transmission assembly 226 shows a monitor photodiode 227, which is connected to a transimpedance amplifier 223 and a transmission controller 229. It is important to note that both analog and digital signals can pass between the controller 229 and the monitor photodiode 227. The transmission controller 229 is connected to the transmission subassembly 222, which will be described in more detail below.

[0048] Various embodiments of the monitored LiDAR system described herein include reference to various controllers. The various controllers control different aspects of the system as described. It should be understood that the description of the controllers does not limit the implementation in any way. The placement of any particular control function within the sensor system and / or monitored LiDAR system can be flexible based on various performance, size, manufacturing, cost, and other constraints of a particular implementation. It should be understood that the controllers described herein can be implemented utilizing the same or different electrical components, processors, and / or circuits, depending on the configuration of the system, in whole or in part, unless expressly stated in the description of a particular embodiment.

[0049] FIG. 2C illustrates an expanded view of the transmit subassembly 222 of FIG. 2B. The transmit subassembly includes a low-side driver 230 on the top edge of a substrate 234, which holds an array of VCSEL laser elements 236. A second low-side driver 230' is positioned on the bottom edge of the substrate 234. The low-side drivers 230, 230' each generate a voltage drive signal in response to a control signal that is appropriate for energizing a laser through a cathode electrode connected to a laser emitter or group of emitters. The address of the control signal indicates the particular cathode electrode, and consequently the laser emitter or group of emitters, that is energized by the low-side drive signal. The high-side driver 232 is positioned on the left edge of the substrate 234, and the second high-side driver 232' is positioned on the right edge of the substrate. In response to the control signal, the high side driver 232, 232' generates a voltage drive signal appropriate for energizing a laser via an anode electrode connected to a laser emitter or group of laser emitters.

[0050] The address of the control signal indicates the particular anode electrode, and consequently the laser emitter or group of emitters, that is energized by the high side drive signal. This particular substrate 234 has 16 anode contacts 238 (only three are depicted) on the left edge of the substrate 234 and 16 anode contacts 238' (only three are depicted) on the right edge of the substrate 234. Similarly, there are cathode contacts 240, 240' located on the top and bottom edges of the substrate 234. The laser elements 236 each have a connection to an anode contact and a cathode contact. A particular row of laser elements is typically connected to either the left high side driver 232 via the anode contact 238 or the right high side driver 232' via the anode contact 238'. A particular column of laser elements is typically connected to either the top side low side driver 230 via the cathode contact 240 or the bottom side low side driver 230' via the cathode contact 240'. It should be understood that numerous other connection patterns are possible. This particular connection pattern is configured such that individual laser elements 236 can be energized by providing drive signals to the high side and low side drivers to which the lasers are connected. The association of anode and cathode contacts that are energized and connected to a group of laser locations or laser emitter locations is given an address.

[0051] FIG. 2D illustrates a close-up view of a high-side current pulse embodiment of a transmit subassembly 250 of the present teachings. The transmit subassembly 250 includes a high-side driver 252, 252' that includes a current pulse generator 253, 253' that connects a high voltage to an anode contact 254, 254'. The current pulse generator 253, 253' is positioned in place of a transistor switch 255 that connects ground to a cathode contact 256 in a low-side driver 257. In this embodiment of the transmit subassembly 250, the low-side driver 257, 257' switches the desired column of laser diode cathodes to ground using a transistor switch 255. The high-side driver 252, 252' drives the appropriate current pulse to the anode of the selected row. The row / column selection is based on the address and the current is based on the desired drive level and / or pulse shape. In some embodiments, the current pulse generator 253, 253' generates a current-limited pulse to the anode. The operation of the low side drivers 257, 257' is similar to that of the low side drivers 230, 230' described in connection with the transmit subassembly 222 of Figure 2C. The high side drivers 232, 232' of the transmit subassembly 222 also operate as switches or selectors and do not provide current limiting pulses as provided by the high side drivers 252, 252' of the transmit subassembly 251 embodiment of Figure 2D. Placing a current driver on the low side is also a possibility.

[0052] FIG. 2E illustrates a close-up view of a low-side current pulse embodiment of the transmit subassembly 260 of the present teachings. The high-side drivers 262, 262′ connect to the anode contacts 263, 263′ using transistor switches 264, 264′. Thus, the laser row that is connected to the high-side voltage is selected based on the row address of the appropriate connection, for example, similar to the switch-based version of the driver in FIG. 2C. The low-side drivers 265, 265′ connect to the cathode contacts 266, 266′ using current pulse generators 267, 267′, which may be current-limited pulse drivers. Thus, the current drive to the columns is controlled by the address that selects the column. The current pulse to the columns can also be set by a drive controller (not shown) that is connected to the low-side drivers 265, 265′.

[0053] The number of driver, contact, and / or laser emitter elements is not limited to those shown in the various embodiments described herein. Typically, much larger arrays and numbers of elements are used in practice to build state-of-the-art systems. Also, while the description presented herein generally refers to elements in a two-dimensional array, it should be understood that the present teachings are not so limited and that the features may also be applied to one-dimensional emitter arrays, single emitters, and groups of emitters that are not formed into an array, as will be understood by those skilled in the art.

[0054] FIG. 2F illustrates an exemplary embodiment of a failure mode for light output as a function of time related to eye safety for a monitored LiDAR transmitter embodiment of the present teachings. The desired light output as a function of time is shown in a first trace 282. To achieve maximum performance, LiDAR systems typically operate very close to the eye safety threshold, and thus deviations from the operating point may result in the safety threshold being exceeded. System-level eye safety is provided by two standards. In the United States, IEC 60825 eye safety class 1, ANSI Z136.1 and FDA / CDRH 21 CFR 1040 are applicable. These safety limits are related to the light energy of the pulse incident on the eye. Thus, both the duration (width) of the pulse, i.e., repetition rate, and the peak power of the pulse are incorporated into the eye safety threshold determination.

[0055] A common eye safety hazard to consider is a single pulse that is too long, shown in the second trace 284. The third trace 286 shows multiple pulses in a repeating pattern that are too long. Another common eye safety hazard to consider is a pulse that has excessive peak power. The fourth trace 288 shows a pulse with too much peak power. Yet another common eye safety hazard to consider is a repetition rate (or duty cycle) that is too high. The fifth trace 290 shows a pulse with too high a repetition rate. All these eye safety hazards would result in more energy per time period than the desired light output in the first trace 282. These failures of increased pulse duration and / or increased repetition rate can be detected using a time-to-digital converter, as further described below.

[0056] FIG. 3 illustrates an embodiment of the transmit electronics 204 of the LiDAR transmit and receive system described in connection with FIG. 2A. The transmit electronics provide a parallel set 302 of connections from a high-side laser driver 304 to individual laser array anode contacts. The anode contacts connect to specific groups of emitters depending on the design. The transmit electronics provide a parallel set 306 of connections from a low-side laser driver 308 to laser array cathode contacts. The cathode contacts connect to specific groups of emitters depending on the design. The outputs of the high-side laser driver 304 and the low-side laser driver 308 are also connected to a diagnostic module 310. A digital logic circuit 312 provides control signals to the high-side laser driver 304 and / or the low-side laser driver 308, including the address of the laser or group of emitters in the array to fire and the desired drive voltage to be applied to the contacts associated with that address. The digital logic 312 also provides this information to the diagnostic module 310. The digital logic 312 receives inputs from a monitor (optional) and provides inputs and outputs to a controller. The controller can be, for example, the controller 202 described in connection with FIG. 2A. The digital logic 312 is also connected via inputs and outputs to a receiver module. The receiver module can be, for example, the receiver module 208 described in connection with FIG. 2A.

[0057] It should be understood that the digital logic circuitry 312 may also contain analog circuitry and provide analog signal inputs and outputs. For example, a monitor photodiode, generally configured as an analog device, may interface with the digital logic circuitry 312. It should be understood that the term "digital logic," as used in connection with the monitoring system of the present teachings, includes the implementation of simple low-cost circuits, logic elements, and comparators that provide rapid and accurate identification of and reaction to fault conditions.

[0058] An optional temperature sensor 314 with a thermal sensor can be placed in proximity to the laser array. The output of the temperature sensor 314 connects to the diagnostic module 310. In some embodiments, the temperature sensor 314 can be part of the high side driver and / or the low side driver. For example, this includes any or all of the drivers 230, 230', 232, 232', 252, 252', 257, 257', 262, 262', 265, 265' shown in Figures 2C-E.

[0059] Figure 4 illustrates one embodiment of a diagnostic module 310 of an embodiment of the transmission electronics 204 described in connection with Figure 3. Digital electronics 402 is fed input signals from the high side and low side controls, including addresses and desired drive voltage levels, provided by digital logic circuitry 312, described in connection with Figure 3. There are also inputs and outputs to the digital logic circuitry 312 for the transmission of other signals between the digital electronics 402 and the digital logic circuitry 312.

[0060] The digital electronics 402 can include a digital comparator. A time-to-digital converter (TDC) 404 is connected to the digital electronics 402. The TDC 404 can provide information regarding the pulse duration and / or repetition rate of both the desired laser drive voltage (or current) for the high side and low side and the actual high side and low side drive voltage (or current) provided to the laser and digital electronics 402. In this manner, simple logic operations performed by the digital electronics 402 can provide fault information related to meeting eye safety requirements as described herein.

[0061] The physical high side signal drive voltage (parallel lines) and the physical low side signal drive voltage (or current) (parallel lines) are passed through electrical circuits 405, 406, which may be voltage attenuators and / or current monitors, to analog-to-digital converters (ADCs) 408, 410 and to one input of comparators 412, 414. In embodiments that use current monitoring in the electrical circuits 405, 406 that pass the physical signal drive currents, the ADCs 408, 410 sample the peak current using a sample and hold. The current monitor electrical circuits 405, 406 can be current mirror circuits.

[0062] The comparators 412, 414 are analog comparators. In some embodiments, the ADCs 408, 410 are multi-channel low-speed ADCs. In some embodiments, the comparators 412, 414 are multi-channel comparators. A second input of the comparators 412, 414 is provided with an analog voltage by a digital-to-analog converter (DAC) 416, 418, which is connected to the digital electronics 402. In some embodiments, the ADCs 408, 410 are multi-channel low-speed ADCs. The digital-to-analog converters 416, 418 provide threshold voltages to be compared in the comparators 412, 414. In this configuration of the diagnostic module 310, simple logic operations in the digital electronics 402 using the outputs of the comparators 412, 414 and / or the ADCs 408, 410 can detect various faults and provide fault indicators therefor to the digital logic 312 (FIG. 3). Exemplary faults include a shorted VCSEL in the array matrix, excessive VCSEL leakage current, a VCSEL reverse breakdown voltage that is too low, a high-side channel (anode) stuck at a high voltage, a high-side channel (anode) being driven by more than the desired voltage set by the digital logic 312, a low-side channel (cathode) stuck at ground, and a low-side channel (cathode) at less than the desired voltage set by the digital logic 312.

[0063] Another feature of the present teachings is that it can be used with different architectures and / or implementations of high-side and / or low-side drivers connected to a matrix-driven VCSEL array. In addition, high-side only and low-side only configurations can also be used. The drivers can be located on one or both sides of the VCSEL array.

[0064] 5A illustrates one embodiment of a transmission subassembly for a VCSEL array for a monitored LiDAR transmitter of the present teachings. The VCSEL array 502 has a column of laser emitters 504, 506 with anodes connected to a high-side driver 508 located on the top side of the array 502, and another column of laser emitters 510, 512 connected to a high-side driver 514 located on the bottom side of the array 502. The VCSEL array 502 has a row of laser emitters 516, 518 with a cathode connected to a low-side driver 520 located on the left side of the array 502. The other row of emitter cathodes is connected to a low-side driver 522 on the right side of the array 502. A 2×2 configuration of drivers 508, 514, 522, 522 is shown for simplicity, but an N×M configuration can also be used, which is both much larger and more generalized.

[0065] In some embodiments, the driver chips, including the high-side and low-side drivers 508, 514, 520, 522, are placed as close as possible to the VCSEL array 502 for low inductance and good electrical performance. The close proximity of the drivers 508, 514, 520, 522 and the array 502 can also improve the ground return path under the matrix array 502.

[0066] Referring back to FIG. 4, in some embodiments, the diagnostic module 310 is physically part of the same chip as the analog driver circuits of the high-side and low-side drivers 508 , 514 , 520 , 522 .

[0067] Another feature of the present teachings is that various processing electronics and control functions may be shared as desired. Figure 5B illustrates one embodiment of a transmit subassembly 530 for a VCSEL array 534 for a monitored LiDAR transmitter with a shared integrated circuit chip 532 for the low-side and high-side drivers of the present teachings. The VCSEL array 534 has four rows 536 of emitters, each connected to a common cathode electrode contact 538 and driven by one of four low-side drivers 540 in a quadruple low-side driver section of the chip 532.

[0068] The VCSEL array 534 has four columns 542 of emitters, each connected to a common anode electrode contact 544 and driven by one of four high-side drivers 546 in a quad-low-side driver section of the chip 532. The chip 532 also contains electronic components in a shared diagnostic section 548. For example, the shared diagnostic section 548 may include all or part of the functions in the diagnostic module 310 described in connection with Figures 3 and 4 and / or the simple logic operations in the digital electronics 402. This configuration may advantageously reduce the size, cost, and / or complexity of the subassembly 530.

[0069] 5C illustrates one embodiment of a transmit subassembly 560 for a VCSEL array 576 for a monitored LiDAR transmitter with separate diagnostic circuits 562, 564 for the low-side and high-side drivers of the present teachings. Two separate chips 566, 568 are used to implement the diagnostic circuits 562, 564. One chip 568 includes four high-side driver circuits 570, each connected to a common anode contact 572 that connects a column 574 of emitters in the VCSEL array 576. The second chip 566 includes four low-side driver circuits 578, each connected to a common cathode contact 580 that connects a row 582 of emitters in the VCSEL array 576. Each chip 566, 568 also contains electronic components for a separate high-side or low-side driver side in separate diagnostic sections 564, 562. Each of the separate diagnostic sections 564, 562 may include all or some of the functionality in the diagnostic module 310 and / or simple logical operations in the digital electronic device 402, described in connection with Figures 3 and 4. This configuration may advantageously reduce the size, cost, and / or complexity of the transmission subassembly 560 and improve its layout alignment.

[0070] 5B-5C, as an example, a comparator in a diagnostic circuit associated with the high side, either the shared circuit 548 or the separate diagnostic circuit 562, compares each output voltage provided by the high side drivers 546, 570 with a high threshold voltage of a predetermined value, referred to as TH_HIGH. The comparator output can be latched into a register after a predetermined delay time from enabling the high speed drivers 546, 570. The latched result is bit-XORed with the address bits in the shared diagnostic circuit 548 or the separate diagnostic circuit 562 and masked with an optional mask bit. The result can be stored in an error sticky bit in the shared diagnostic circuit 548 or the separate diagnostic circuit 562 until it is read by an upstream controller (not shown in FIGS. 5B-C).

[0071] In operation, if the error bit is high, this indicates an error condition for two example cases that are described in detail below. A first example is that if the high side emitter at an address (also called a channel) is higher than TH_HIGH, this indicates that the channel is active while a different channel is selected (or stuck at the high channel), thus indicating an error in channel selection. A second example is that if the high side channel is lower than TH_HIGH and this channel is selected, this indicates a bad high side channel. This could mean, for example, a short circuit or a short with an adjacent channel.

[0072] FIG. 6 illustrates a table 600 showing an example embodiment of fault criteria, faults, and controller responses for idle operation for a monitored LiDAR system of the present teachings. Example faults that may be identified include various shorts of VCSEL anode and / or cathode contacts, excessive leakage current in the VCSEL, excessive leakage current above a threshold level in the VCSEL, and the cathode and / or anode stuck at a high voltage. Various threshold voltages (V1, V2, V3, V4, V5, V6, V7, V8, V9, and V10) are shown as some of the various fault criteria that may be used to identify the corresponding faults. This representation serves to show that these voltages may be independently selected, and not necessarily that they are different values. For example, as described herein, those voltages that represent lower values ​​of array cathode and / or anode voltages may all share a common value of a low voltage threshold. For example, different sections of the array may have different or the same values ​​of threshold voltages for the lower end of the range, as desired. This may be, for example, TH_LOW in the examples herein. For example, as described herein, all of the voltages representing higher values ​​within the range of array cathode and / or anode voltages may share a common value of a high voltage threshold. This may be, for example, TH_HIGH in the examples herein. In addition, TH_HIGH and TH_LOW thresholds may be applied to the anodes and / or cathodes as described. In some embodiments, TH_HIGH for the anodes will have a different value than TH-HIGH for the cathodes, and TH_LOW for the anodes will have a different value than TH-LOW for the cathodes.

[0073] Various actions can be taken in response to identifying a fault. Referring to FIG. 2A, actions can be taken by any or all of the transmission electronics and laser driver 204, the controller 202, and / or the host processor 214, as appropriate. Exemplary actions include those listed in table 600, and in addition, displaying a warning message, performing a shutdown of all or a portion of the laser emitter and / or associated driver, making changes to the emitter firing pattern, repurposing parts of the array and its control scheme, and implementing other actions.

[0074] One feature of the present teachings is that the monitored transmitter can identify faults associated with the electrode side (or sides) driven on the high side of the anode of the VCSEL array. FIG. 7 illustrates a table 700 showing an example embodiment of fault criteria, faults, and controller responses for active operation in a high side drive for a monitored LiDAR system of the present teachings. With reference to FIGS. 3 and 4, a logic fault or a short between the VCSELs can be indicated if the anode drive voltage generated by the high side driver 304 does not match the command desired drive voltage generated by the digital logic 312 as determined by the digital electronics 402. These two types of faults can be distinguished, for example, by comparing adjacent array elements (and / or driver addresses). The digital electronics 402 can identify the fault. The digital electronics 402 and / or digital logic 312 can then take action to disable the faulted channel if a short is found. The digital electronics 402 and / or digital logic 312 may also take appropriate action to correct a logic failure or addressing failure if that is the reason determined to be due to a voltage mismatch.

[0075] In addition, the monitored transmitter of the present teachings can find faults in the drivers. For example, a bad anode high side driver can be determined if the active anode channel voltage is below the TH_HIGH threshold level for the anode. In this case, the output of the high side driver 304, as measured by the diagnostics section 310, is producing a voltage that is less than the desired voltage.

[0076] FIG. 8A illustrates a graph 800 showing the time dependence of good active and inactive channels and high thresholds at the anode for a monitored LiDAR system of the present teachings. The top graph 802 illustrates the timing of a control pulse to energize a particular emitter at a particular address. The bottom graph 804 shows an example high side voltage as a function of time generated by the laser driver in response to the control pulse. A voltage pulse for a good active channel 806 is shown, which is for a channel addressed by the controller. In addition, a voltage pulse for a good inactive channel 808 is also shown, which is for a channel not addressed by the controller. A TH_HIGH threshold voltage is also shown (810). Referring to FIGS. 3 and 4, the comparator 412 compares the anode voltage (good active channel 806) with a predetermined value, i.e., TH_HIGH, after a delay 812. The delay 812 is chosen so that the sampled voltage of the active channel 806 is after any expected rise time. The value of the voltage of the good active channel 806 does not fall below TH_HIGH. As a result, the output of the comparator 412 is not latched into the fault register after the predetermined delay time because the good active channel voltage 806 exceeds TH_HIGH.

[0077] In general, the monitoring system captures the state of the anode drive voltage during firing or energization of the laser and compares this to the desired state at a point in time between firings. This process captures fault conditions within various components such as the laser array, the electrodes and other electrical connections, the driver circuitry, and / or the digital logic that controls the driver. The monitoring system does not need to react to conditions that represent good operation.

[0078] 8B illustrates a graph 850 showing the time dependence of bad active and inactive channels and high thresholds at the anode for a monitored LiDAR system of the present teachings. The top graph 852 illustrates the timing of control pulses to energize a particular emitter located in the array as represented by a particular address. The bottom graph 854 shows an example high side voltage as a function of time generated by the laser driver in response to the control pulse. A voltage pulse for a bad inactive channel 856 is shown on the graph, which is for a channel not addressed by the controller. A voltage pulse for a bad active channel 858 is also shown on the graph. An active channel refers to a channel that is addressed by the controller.

[0079] The TH_HIGH threshold voltage is also shown as 860. Also referring to Figures 3 and 4, the comparator 412 compares the anode voltage (e.g., the bad inactive channel 856) to a predetermined value, i.e., TH_HIGH, after a delay 862. The delay 862 is chosen so that the sampled voltage of the inactive channel 856 is after any expected rise time. The voltage of the bad inactive channel 856 exceeds TH_HIGH. The output of the comparator 412 is latched into a fault register after the predetermined delay time, detecting a fault. This could be, for example, an addressing error where the actual drive voltage for the VCSEL at an address is driven high even though the controller wanted the VCSEL at that address to be low or inactive.

[0080] Note that a bad active channel condition 858 is not identified by a comparison of the TH_HIGH voltage. For this type of fault, a TH_LOW threshold is implemented. In general, the monitoring system captures the state of the anode drive voltage during the firing or energization of the laser and compares this to the desired state at a time during firing. This can include providing both TH_HIGH and TH_LOW for each driver. Also referring to FIG. 4 as an example, when the comparison results in a deviation beyond a set threshold, the output of the comparator 412 is latched into a fault register after a predetermined delay time if the comparator determines a fault. In general, in many embodiments, the monitoring system captures the state of the actual drive voltage during the firing or energization of the laser and compares this to the desired drive voltage for a particular laser address at a time that occurs during firing, which may be a delay after the issuance of the energization control signal. Inactive (unaddressed) channels can also be monitored in this manner. This process can efficiently and effectively capture fault conditions within the laser array, electrodes, and other electrical connections, driver circuits, and / or digital logic that controls the drivers.

[0081] As described herein, the high side drive connected to the anode contact can use both high and low threshold voltages. FIG. 9 illustrates a table 900 showing an example embodiment of fault criteria, faults, and controller responses for a low voltage threshold at the anode for a monitored LiDAR system of the present teachings. A VCSEL array anode drive voltage above the low voltage threshold can indicate a logic or addressing fault, a short between array channels, or a fall error from a previously energized array element. The controller or system can react by disabling the failed channel. In addition, increasing the firing time period can also be implemented, for example, if a previous channel is found to fall during a subsequent activation cycle. In this case, extending the time between firings can avoid this problem.

[0082] FIG. 10A illustrates a graph 1000 showing good active and inactive channels and the time dependence of thresholds at the anode low voltage threshold for a monitored LiDAR system of the present teachings. The top graph 1002 illustrates the timing of a control pulse to energize a particular emitter located in the array as represented by a particular address. The bottom graph 1004 shows an example high side voltage as a function of time generated by the laser driver in response to the control pulse. A voltage pulse as a function of time for a good active channel 1006 is shown. A good active channel means a channel that is addressed by the controller. A voltage pulse for an inactive channel 1008, which would be considered good, is also shown in addition to the TH_LOW threshold voltage 1008. It is important that the inactive channel remains below the TH-LOW voltage 1008 as measured at a selected delay 1010 after the start of the energization control information shown in the top graph 1002.

[0083] FIG. 10B illustrates a graph showing the time dependence of a bad inactive channel and threshold at the anode low voltage threshold for a monitored LiDAR system of the present teachings. The top graph 1052 illustrates the timing of a control pulse to energize a particular emitter located in the array as represented by a particular address. The bottom graph 1054 shows an example high side voltage as a function of time generated by the laser driver in response to the control pulse. A voltage pulse 1056 as a function of time for a bad inactive channel having a too slow fall is shown as is the TH_LOW threshold, which is compared at a delay 1060 after the control pulse generation. The voltage pulse 1056 as a function of time for a bad inactive channel will exceed the TH_LOW value.

[0084] In some embodiments, a comparator compares each output voltage for a given channel to a predefined value (TH_LOW) 1058. The output of the comparator is latched into a register after a predefined delay from enabling the control pulse. In this case, it would be for a channel that is inactive but is supposed to exhibit a voltage exceeding TH_LOW. The latched result can be bit-XORed with the address bit and masked with an optional mask bit, and the result can be stored in the error sticky bit. If the error bit is high, it will indicate a fault in at least two cases. First, if the anode high driven channel output is higher than TH_LOW and the channel is supposed to be inactive (i.e., a different channel was selected), this condition could mean either a slow fall of the previously selected HS channel or an error in the channel selection. If the anode high driven channel output is lower than TH_LOW even though this channel was selected to be active, this indicates a bad channel, which could be a short circuit or a short with an adjacent channel.

[0085] Another feature of the present teachings is that it can monitor the cathode electrode of the LiDAR transmitter and / or the anode electrode driven on the high side at multiple points of the system, including the LiDAR transmitter on the low side. FIG. 11 illustrates a table 1100 showing an example embodiment of fault criteria, faults, and controller responses for an active channel at the cathode at the low voltage threshold for a monitored LiDAR system of the present teachings. Fault criteria can include a cathode drive voltage not meeting a desired control voltage. This can indicate faults such as logic failures and shorts between VCSEL array channels. In these cases, the controller can diagnose the fault and / or disable the faulted channel. Another fault criterion is when an active channel at the cathode is presented with a drive voltage above a threshold voltage. This condition can be caused by a bad cathode driver and can be remedied by disabling the faulted channel.

[0086] 12A illustrates a graph 1200 showing good active and inactive channels and the time dependence of thresholds at the cathode low voltage threshold for a monitored LiDAR system of the present teachings. The top graph 1202 illustrates the timing of a control pulse to energize a particular emitter at a particular address. The bottom graph 1204 shows an example low side voltage as a function of time generated by the low side laser driver in response to the control pulse. A voltage pulse for a good active channel 1206 is shown, which is for a channel addressed by the controller. A voltage pulse for a good inactive channel 1208 is also shown, which is for a channel not addressed by the controller. A TH_LOW threshold voltage is also shown (1210).

[0087] 3 and 4, the comparator 414 compares the cathode voltage due to the low side driver 308 (e.g., good active channel 1206) to a predetermined value, i.e., TH_LOW 1210, after a delay 1212. The condition for TH_LOW and the particular drive signal is related to a particular control signal provided by the digital logic 312. The delay 1212 is chosen so that the sampled voltage of the active channel 1206 is after any expected reaction time for a voltage level change. The value of the voltage of the good active channel 1206 falls below TH_LOW. The trace 1208 of the good inactive channel is also above TH_LOW. The output of the comparator 414 is not latched into the fault register after the predetermined delay time because the good active channel voltage 1206 falls below TH_LOW. In general, the monitoring system captures the state of the cathode drive voltage during the firing or energization of the laser and compares this to the desired state as indicated by the control pulse at a time during the firing. The process captures fault conditions within the laser array, the electrodes and other electrical connections, the driver circuitry, and / or the digital logic that controls the driver. The process can also be configured to be unresponsive to non-fault conditions.

[0088] 12B illustrates a graph 1250 showing the time dependence of the thresholds for bad active and inactive channels at the cathode low voltage threshold for a monitored LiDAR system of the present teachings. The top graph 1252 illustrates the timing of control pulses to energize a particular emitter located in the array as represented by a particular address. The bottom graph 1254 shows an example of a low side voltage as a function of time generated by the laser driver in response to a control pulse. A voltage pulse for a bad inactive channel 1256 is shown, which is for a channel not addressed by the controller. A voltage pulse for a bad active channel 1258, which is for a channel addressed by the controller, is also shown in addition to the TH_LOW threshold voltage 1260.

[0089] 3 and 4, the comparator 414 compares the cathode voltage generated by the low side driver 308 (e.g., the bad inactive channel 1256) to a predetermined value, i.e., TH_LOW, after a delay 1262. The delay 1262 is selected such that the sampled voltage of the inactive channel 1256 is after any expected reaction time to a fire control signal.

[0090] In a fault condition, the voltage of the bad inactive channel 1256 falls below TH_LOW. The output of the comparator 414 is latched into a fault register after a predetermined delay time, detecting a fault on the address of this inactive channel. The voltage of the bad active channel 1258 rises above TH_LOW. The output of the comparator 414 is latched into a fault register after a predetermined delay time, detecting a fault on the address of this active channel.

[0091] 13 illustrates a table 1300 showing an example embodiment of fault criteria, faults, and controller responses for active channels at a high voltage threshold for the cathode for a monitored LiDAR system of the present teachings. Comparing the cathode voltage to the high voltage threshold, i.e., TH_HIGH, can identify faults such as logic faults, addressing faults, and / or shorts between VCSEL array channels. The controller can respond by disabling the failed channel or resetting the address.

[0092] 14A illustrates a graph 1400 showing good active and inactive channels and the time dependence of thresholds at the high voltage threshold at the cathode for a monitored LiDAR system of the present teachings. The top graph 1402 illustrates the timing of a control pulse to energize a particular emitter at a particular address. The bottom graph 1404 shows an example low side voltage as a function of time generated by the low side laser driver in response to the control pulse. A voltage pulse for a good active channel 1406 is shown, which is for a channel addressed by the controller. A voltage pulse for a good inactive channel 1408 is also shown, which is for a channel not addressed by the controller. A TH_HIGH threshold voltage is also shown (1410).

[0093] 3 and 4, the comparator 414 compares the cathode voltage by the low side driver 308 (e.g., the good active channel 1406) to a predetermined value, i.e., TH_HIGH 1210, after a delay 1412. The condition for TH_HIGH and a particular drive signal is related to a particular control signal provided by the digital logic 312. The delay 1412 is chosen such that the sampled voltage of the active channel 1406 is after any expected reaction time for a voltage level change. The value of the voltage of the good active channel 1406 falls below TH_HIGH. The trace 1408 of the good inactive channel is above TH_HIGH. As a result, the output of the comparator 414 is not latched into the fault register after the predetermined delay time because the good active channel voltage 1406 falls below TH_HIGH, and so does the good inactive channel.

[0094] 14B illustrates a graph 1450 showing the time dependence of the threshold for a bad inactive channel and the high voltage threshold at the cathode for a monitored LiDAR system of the present teachings. The top graph 1452 illustrates the timing of a control pulse to energize a particular emitter located in the array as represented by a particular address. The bottom graph 1454 shows an example of a low side voltage as a function of time generated by the laser driver 308 in response to a control pulse. A voltage pulse for a bad inactive channel 1456, which is for a channel not addressed by the controller, is also shown in addition to the TH_HIGH threshold voltage 1458.

[0095] 3 and 4, the comparator 414 compares the cathode voltage generated by the low side driver 308 (e.g., the bad inactive channel 1456) with a predetermined value, i.e., TH_HIGH, after a delay 1460. The delay 1460 is selected such that the sampled voltage of the inactive channel 1456 is after any expected reaction time to a fire control signal. The voltage of the bad inactive channel 1456 falls below TH_HIGH. The output of the comparator 414 is latched into a fault register after the predetermined delay time, detecting a fault for the address of this inactive channel.

[0096] One feature of the present teachings is that it can provide fault monitoring based on timing errors in the LiDAR transmitter, separate from or in addition to voltage threshold based criteria. Figure 15 illustrates a table 1500 showing an example embodiment of faults and controller reactions related to monitored pulse widths for a monitored LiDAR system of the present teachings. Multiple TDCs (Time / Digital) can be used to monitor system timing such as propagation delay, pulse width (or duration), and pulse period. All of these can be compared to desired values. Below are some examples.

[0097] If the pulse duration of the active channel is determined to be too short, the pulse width can be increased. If the pulse duration of the active channel is determined to be too long, the system can further determine whether eye safety limits have been exceeded and can shut down the active element in response. If the pulse duration is too long but still safe, the reaction can be different. For example, the reaction can be to shorten the pulse but shut down the laser element to keep the system operation high performance. In some embodiments, synchronization pulses are used and these can also be checked using TDC to determine whether the pulse is too short or too long to the extent that it triggers a fault condition so that corrective action can be taken within these fault conditions.

[0098] FIG. 16 illustrates a graph 1600 showing the time dependence of a pulse in a high side drive at an anode for a monitored LiDAR system of the present teachings. The top graph 1602 illustrates the timing of a control pulse to energize a particular emitter at a particular address. The bottom graph 1604 shows an example high side voltage pulse as a function of time generated by a laser driver in response to a control pulse. A series of different delays 1606 from the generation of the control pulse, namely delay 1, delay 2, ... delay 10, are used to search for the pulse at different times. Different high voltage thresholds, namely TH_HIGHX (where X=1, 2, 3, ... 10), are used for the different delays. This allows for a more detailed extraction of the high side or low side electrical pulse shape. This more detailed time-based extraction of the voltage allows for more sophisticated conditions to be established. For example, a successive approximation algorithm can be used to find the voltage level at a given delay. This can be used for several purposes. For example, time-based thresholding can be used during electrical turn-up of a printed circuit board assembly. Time-based thresholding can be used for system delay adjustment. By extracting the high-side pulse shape, the system can determine the delay required between the high-side control and the low-side control. During an extensive system test at power-on, each channel pulse shape can be diagnosed to find the faulty channel. For example, the fault can be based on a rise time and / or fall time of the pulse voltage that is too slow or too fast. It should be understood that FIG. 16 and the corresponding description teaching the use of delays in connection with the case of high-side drive pulses can be similarly applied to time-based thresholding and fault condition detection for low-side drive pulses.

[0099] FIG. 17 illustrates a timing diagram 1700 for high side drive 1702 and low side drive 1704 and light pulse 1706 of an embodiment of a monitored LiDAR system of the present teachings. There are three main regions of operation illustrated in this embodiment. A system power-on region 1708 can include extensive diagnostics of drivers associated with all or some of the VCSEL matrix, individual elements, and addresses. The power-on region can be followed by normal operation regions 1710, 1710′. These normal operation regions 1710, 1710′ can be separated by running diagnostic regions 1712, 1712′. In the normal operation regions 1710, 1710′, real-time diagnostics are performed on the live laser drive signal. A property of this region 1710, 1710′ is that the system avoids firing any laser that is not part of acquiring scene data. The active diagnostics region 1712, 1712' differs from the normal operation region 1710, 1710' in that test firing of the laser is permitted.

[0100] An exemplary operation of a monitored LiDAR transmitter of the present teachings can be described in the following manner: The laser transmission logic / controller (e.g., digital logic 312 of FIG. 3, or controller interface 202 of FIG. 2, or both) counts the number of shots (i.e., laser drive pulses applied). The host (e.g., host 214 of FIG. 2) compares the count to the number of actual shots (i.e., laser pulses emitted). The laser transmission logic / controller calculates the shot energy (number of pulses at a given time) and stops the shot if eye safety limits are exceeded.

[0101] The pulse duty cycle is diagnosed using an energy-related mechanism as determined by the TDC. For example, a moving average can be calculated by counting the number of pulses in each predetermined window. If the count value exceeds a predetermined threshold, an error flag is raised. In some embodiments, a digitally oriented calculation method such as a "leaky bucket" can be used. The use of a TDC allows for the determination of actual current pulse width, propagation delay diagnosis, and conformance. In these embodiments, the TDC is connected to a digital comparator that generates a fail-high error and a fail-low error. The use of a TDC allows for the calibration of each individual VCSEL propagation delay, which can improve the calibration of the system. In addition, by using a TDC, the actual pulse count value can be diagnosed and compared to an expected pulse count value.

[0102] Another feature of the apparatus and method of the present teachings is that it allows LiDAR performance to be tailored for specific desired operational performance and reliability. The Society of Automotive Engineers (SAE) defines six levels of driving automation ranging from 0, i.e. fully manual, to 5, i.e. fully autonomous. For levels 0-2, a human driver monitors the driving environment. For levels 3-6, an automated system monitors the driving environment with various levels of accuracy and functionality.

[0103] Surveillance is performed through a combination of different sensors and technologies such as radar, cameras, and sonar for detection and location of surrounding objects. Among these sensor technologies, Light Detection and Ranging (LiDAR) systems play a key role as they enable real-time, high-resolution 3D mapping of the surrounding environment.

[0104] Sensors targeted for use within autonomous driving must typically comply with international safety standards, such as the International Organization for Standardization (ISO) 26262 standard, entitled "Road Vehicles - Functional Safety," first defined in 2011 and revised in 2018. Functional safety is the part of the overall safety of a system or piece of equipment that relies on automatic protection. Automatic protection systems are designed to respond to various types of system failures to prevent possible hazards or reduce their severity. System failures can result from human error, hardware failures, and operational / environmental stresses.

[0105] The ISO 26262 standard addresses the possible hazards caused by malfunctions of electronic and electrical systems in passenger vehicles as determined by the Automotive Safety Level ("ASIL"). ASIL addresses four different risk levels (A, B, C, and D) that are determined by three factors: (1) exposure (probability of the hazard), (2) controllability (whether the driver can respond to the hazard), and (3) severity (type of injury). The ASIL risk level is broadly defined as a combination of severity, exposure, and controllability.

[0106] LiDAR sensors must also comply with international standards for eye safety because they incorporate at least one laser. Regulations have been established to set standards for acceptable amounts of laser radiation to ensure that products are labeled in a manner that consumers understand the safety risks associated with a particular product. The most referenced standard throughout the world is the IEC 60825-1 standard, published by the International Electrotechnical Commission (IEC), which has been adopted as the EN 60825-1 standard in Europe. In the United States, laser products are covered by the CDRH 21 CFR 1040.10 standard, and compliance with the 60825-1 standard has been established as acceptable to meet US Federal standards.

[0107] These eye safety standards classify lasers into different safety categories according to their wavelength and maximum output power. The standards define the Maximum Permissible Exposure (MPE), defined as the optical power or energy that can pass through a fully dilated pupil without causing any damage.

[0108] In systems where the laser is not operated continuously, but instead is pulsed, the MPE is a function of energy, which is related to the laser pulse duration and duty cycle. Class 1 lasers are safe under all conditions of normal use. The Maximum Permissible Exposure (MPE) cannot be exceeded in a Class 1 product. It is therefore highly desirable for automotive LiDAR systems to be Class 1 eye safe.

[0109] Ensuring that LiDAR systems comply with international safety standards requires a rigorous development process and robust design. Particular attention should be paid to the detection of occurrences of faults and uncontrollable behavior in electronic, optical, and electrical systems that may occur during the system's lifetime. The monitored LiDAR system of the present teachings enables this detection and subsequent reaction to faults and uncontrollable behavior.

[0110] LiDAR systems for autonomous vehicles should also maximize measurement range while maintaining class 1 eye safety. Range is a function of signal-to-noise and therefore will correspondingly increase with maximization of the peak optical power of the transmitting laser. However, class 1 eye safety limits the maximum peak optical power along with the pulse duration / frequency.

[0111] For example, from the IEC 60825-1 standard, it can be calculated that for an exposure duration of 10 picoseconds to 5 μs, the permissible exposure energy for a 903 nm laser would be 0.392 μJoules. Thus, if a single laser pulse of 5 nanoseconds duration is delivered every 5 μs, and the pulse is assumed to be rectangular in shape (zero rise / fall time), the maximum peak power of this pulse would be 78.4 W. Correspondingly, if the rectangular pulse was 50 nanoseconds in duration, the maximum peak power would be one tenth of that, i.e., 7.84 W.

[0112] Lasers capable of achieving these peak powers can typically be used to produce higher light powers as well if supplied with appropriate bias currents. It is important to include optical transmit power monitoring in these LiDAR systems to more clearly know that the light pulse energy (power integrated over time) does not exceed the MPE for Class 1 eye safety. For example, a monitor photodiode 227 as described in connection with FIG. 2B can be used. See, for example, U.S. Patent Application No. 15 / 915,840, entitled "Eye-Safe Scanning LiDAR System," and U.S. Provisional Patent Application No. 63 / 112,735, entitled "LiDAR System with Transmit Optical Power Monitor," both of which are assigned to the present assignee and incorporated herein by reference.

[0113] While optical monitoring provides important feedback for eye safety by itself, additional fault monitoring, as described herein, is also needed to determine additional details that can be used to locate the exact fault condition, notify the host of the fault condition, and / or potentially adapt system operating parameters to compensate or correct the fault. In a multi-laser LiDAR system, there may be short circuits or electrical crosstalk that cause the laser to fire unintentionally. If more than one laser is firing at the same time or close enough in time to another laser, it is necessary to consider their combined energy with respect to addressing eye safety marginal considerations. It may also be important to ensure that the laser is not firing unintentionally through some unintentional crosstalk or electrical short in the electronic circuitry.

[0114] Many LiDAR systems build a 3D point cloud that accurately represents the environment in order to be able to detect and identify objects in the environment. If the 3D data is not accurate or reliable, various types of dangers may arise. For example, if an object is not detected in the path of an autonomous vehicle and the vehicle is moving, a collision may occur, resulting in damage to surveillance and possibly physical harm to individuals. It should be understood that LiDAR sensors have measurement range limitations, so for distant objects and / or low reflectivity objects, at some distance the probability of detection drops to zero. However, missing objects may also be the result of fault conditions in the LiDAR system. For example, LiDAR systems may suffer from "blind spots" during operation, which may be caused by several factors, including the laser not firing accurately, dust or other foreign objects coating the lens, and / or various types of errors in the receiver circuitry. Non-detection may result from a bad active channel, when a return signal is not received from the location for various reasons, including the laser not firing when expected.

[0115] Another potential problem with LiDAR systems is the so-called "false positive", which means that the LiDAR system reports the presence of an object that is not actually there. This can also cause functional safety hazards. For example, in a situation where an object is reported in the path of a moving vehicle, an automatic braking system may be triggered to avoid a potential collision. Unnecessary automatic braking can result in injury to people and the vehicle, especially when the vehicle is traveling at high speed rates. False positives can result from poor inactive channel conditions, for example, when the laser light is reflected from a location that is not actively probed and the received signal cannot be spatially distinguished by the detector array.

[0116] Another aspect related to safety is the availability of the LiDAR system at the time of failure during operation. With regard to a fault condition in the LiDAR system, it is highly undesirable to trigger a complete shutdown of the LiDAR system, since shutting down the LiDAR system would result in the need for service to repair or replace components, with associated costs and inconvenience to the user, especially considering that it is unlikely that any part of the LiDAR system would be user serviceable. A shutdown of the LiDAR system may also result in an unsafe condition and even a complete loss of use of the vehicle. In a fully autonomous vehicle, a shutdown of the LiDAR system would likely disable the vehicle. In any case, any ongoing movement would be adversely affected by the shutdown of the LiDAR system.

[0117] Instead, it is desirable for the LiDAR system to adjust to the obstacle condition in some manner that allows the vehicle to continue to function and complete any movement currently underway. Thus, the ability to isolate the location and / or type of obstacle by the systems and methods of the present teachings is important to the practical commercialization of LiDAR systems.

[0118] Another feature of the present teachings is that multiple system-level responses to a fault condition identified by a monitored LiDAR transmitter can be implemented. For example, at the most basic level, the monitored LiDAR transmitter can notify the host of a fault condition. This is the basic action that the LiDAR system can take, allowing the host system to take action based on the fault information. Decisions can also be made at the LiDAR transmitter level so that the transmitter system continues to function in some manner even after a fault occurs. For example, if eye safety is not violated, the LiDAR transmitter can continue to function under the fault condition while communicating the fault condition to the host and allowing the host to take some additional action (e.g., shutting down the sensor, not using the data, or flagging the data as suspicious, etc.) based on predetermined criteria or some type of computer-based algorithm. It should be understood that numerous types of artificial intelligence algorithms can be used by the host to determine the action to be taken for a particular fault condition.

[0119] One example of an algorithm that may be used by the system to improve performance is an algorithm that may communicate the degree of severity of a fault condition to the host. In this scenario, depending on the severity of the fault condition, the monitored LiDAR system may also make recommendations on actions the host should take. A logic tree in the controller (e.g., controller 202 of FIG. 2) based on the fault condition may be used to provide additional information to the host. That is, not only fault codes but also information related to the health of the transmitter and / or specific lasers, such as the actual output power, the exact point in the FOB that is affected, and potentially recommended actions for the host to take, may be transmitted to the host. It should be noted that various aspects of the performance improving algorithms described herein may be implemented in different circuits and / or controllers in different embodiments of the LiDAR system described herein, as appropriate for a particular function, as would be understood by one of ordinary skill in the art.

[0120] Another example of an algorithm that may be used by the system to improve performance is an algorithm to perform a self-diagnostic function to better assess the fault conditions and / or health of the transmitter, including the individual VCSELs. Also, some diagnostic tools can assess the health of the transmitter and / or VCSEL without generating a light pulse. This means that the transmitter and / or VCSEL can be checked before firing to ensure that any potential damage, danger, explosion, and / or emission will not occur in a faulty transmitter and / or VCSEL.

[0121] One example of an algorithm that can be used by the system to improve performance is an algorithm to perform a self-diagnostic function to better assess fault conditions. When a fault condition occurs, the LiDAR system initiates some type of active self-diagnosis. For example, if a fault condition is detected in which two lasers are firing at the same time instead of one, a receiver scan may be initiated to interrogate a detector in the receiver that is detecting return signals for the two lasers. A monitor photodiode may also be used as part of the diagnostic test. Additionally, an algorithm may be used to change the bias level of a laser to determine if the behavior of the laser changes in some expected way and then act on the resulting test data. Furthermore, an algorithm may fire adjacent lasers or groups of lasers and the actual behavior is compared to some expected behavior to give information about the laser that gave the fault condition and then act on that test data and further be used to diagnose faults in the transmitter.

[0122] Another example of an algorithm that may be used by the system to improve system performance is an algorithm for adapting operating parameters according to a particular fault condition. For example, the system may modify the laser firing sequence to accommodate the fault condition. As one particular example of this, if the fault condition is a single laser in the FOV, the system may modify the laser firing map to not fire the bad laser any more and not waste the time slots allocated to fire the bad laser. Instead, the time slots allocated to fire the bad laser may be used to fire adjacent lasers in the FOV, thus improving the SNR over the area around the "blind spot" caused by the "bad laser".

[0123] Yet another example of an algorithm that can be used to improve the performance of the present system is an algorithm that modifies the mapping of lasers or groups of lasers to receiving detectors to accommodate fault conditions. If a laser significantly degrades or fails, the laser / detector mapping can be changed to eliminate the use of that particular laser for all detectors with which it is associated. Any detectors that were using that laser would be reassigned to adjacent lasers based on the control logic and the geometry and electrical connection pattern of the array. It is also known that at different distances, the optimal mapping option may change due to parallax. Thus, such a change may lead to some reduced optical coupling for at least some portion of the detector array FOV corresponding to a particular laser, but still retain functionality at some ranges. Yet another aspect of the present teachings is to realize that using reassignment, blind spots caused by one or more failed lasers may be made smaller with temporary mapping. Such an approach may work better at shorter ranges because the blind spots would be larger at longer ranges.

[0124] One feature of the system and method for active fault monitoring of the present teachings is that it can detect fault conditions and / or perform diagnostics on health conditions in a Light Detection and Ranging (LiDAR) transmitter, and the detected conditions can be reported to other systems in the vehicle and / or to an operational control system or host system in the LiDAR. For example, an embodiment of the method can report the address and fault condition to a host that takes action on the LiDAR transmitter in response to the fault condition. The severity of the error can also be reported. The health of individual VCSELs, groups of VCSELs, and / or the transmitter can also be reported. For example, if the system detects that a particular laser is believed to be degraded in performance but has not yet failed, the health of the laser can be reported to the host as an early warning so that subsequent maintenance or further diagnostics can be performed prior to further degradation. This reporting capability can be useful as part of a functional safety system, as it allows the health and / or failure of a LiDAR transmitter to be included as part of a larger system that impacts the safety of the vehicle. For example, some embodiments of the methods of the present teachings can support the safety lifecycle of a vehicle, including management, development, production, operation, maintenance, and decommissioning, e.g., via reporting steps and / or automated responses to self-diagnosis. Some embodiments of the methods of the present teachings can support the determination of risk classes and / or the provision of requirements associated with achieving acceptable risk levels, e.g., via reporting steps and / or automated responses to self-diagnosis.

[0125] (Equivalent) While the applicant's teachings are described in conjunction with various embodiments, it is not intended that the applicant's teachings be limited to such embodiments. Rather, the applicant's teachings encompass various alternatives, modifications, and equivalents, which may be made therein without departing from the spirit and scope of the present teachings, as will be understood by those skilled in the art.

Claims

[Claim 1] The invention described in this specification.

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