Detector system comparing pixel response with light energy decay.

Abstract

A method and apparatus for controlling a stimulus source to send photons toward pixels in a pixel array included in a detector system, analyzing the response of the pixels in the pixel array, and generating an alert based on the response of the pixels in the pixel array. Exemplary stimulus sources include conductive traces, PN junctions, and current sources.

Description

[Background technology]

[0001] As known in the art, some known ranging systems can include laser radar (ladar), light-detection and ranging (lidar), and distance measurement systems to measure distances to objects in a scene. Laser ranging imaging systems emit pulses toward a specific location and measure the returning echo to estimate distance.

[0002] Traditional laser ranging systems generally work by sending out a laser pulse and recording the time it takes for the laser pulse to reach the target, reflect, and return to a receiver. The laser ranging instrument records the time of the outgoing pulse and the time the laser pulse returns. The difference between these two times is the flight time to the target and back. Using the speed of light, the round trip time of the pulse is used to calculate the distance to the target. Summary of the Invention

[0003] Exemplary embodiments of the present disclosure provide methods and apparatus for optical integrated circuits, such as readout integrated circuits (ROICs), that include safety features, such as Automotive Safety Integrity Level (ASIL)-related features. In some embodiments, one or more features are incorporated into the ROIC to enable ASIL compliance of optical receivers for use in various applications, such as automotive applications.

[0004] The optical system can include a detector pixel with thin conductive traces for generating light energy at the sensitivity level of the optical system. In some embodiments, an LED is positioned near the detector pixel to generate photons in response to an electrical signal. The LED can be located within a package or even external to the receiver system of which the optical ROIC is a part. The ROIC then directly controls the LED output. Direct photon generation can verify the entire receiver signal path. In another embodiment, a voltage is applied to the traces to impose a known voltage. A current source can also be used instead of a pixel.

[0005] In some embodiments, the ROIC generates an alert if it does not detect a return pulse within a certain time window, as opposed to a nominal response of returning no data. In one embodiment, the ROIC applies a known signal to a pixel or pixel array and waits for a response from the pixel and circuitry within the ROIC. In one embodiment, the ROIC can include pulse validation. For example, an alert can be generated if the amplitude of the return pulse over time is not within an expected range. In some embodiments, the shape of the pulse can be evaluated. For example, the pulse shape can be verified to match an expected shape to eliminate possible spurious pulses from the environment overall.

[0006] In some embodiments, the ROIC can include direct electrical stimulation via current generation to verify functionality through a transimpedance amplifier (TIA) via the backend. Dynamic photodetector voltage bias modulation over time can be evaluated low-side by the ROIC to verify that the current response is consistent with a properly functioning photodetector. In some embodiments, the ROIC can include ASIL signal output on multiple or separate pins on the package.

[0007] In one aspect, a method includes controlling a stimulus source to send photons toward pixels in a pixel array included in a detector system, analyzing a response of the pixels in the pixel array, and generating an alert based on the response of the pixels in the pixel array.

[0008] The method may further include one or more of the following features: the stimulus source includes a metal object, and controlling the stimulus source includes heating the metal object; the stimulus source includes a current source; the stimulus source includes a PN junction that provides a light emitting diode (LED); analyzing the response of the pixels in the pixel array includes determining that no response is generated in a predetermined time period corresponding to a predetermined distance; generating the alert based on the response of the pixels in the pixel array corresponds to determining that no response is generated in a predetermined time period corresponding to a predetermined distance; analyzing the response of the pixels in the pixel array includes determining that no response is generated in a predetermined time period corresponding to a predetermined distance after the stimulus source is controlled to send photons toward the pixels in the pixel array to stimulate the pixels to generate a response. the detector system comprises a photodiode coupled to an amplifier that provides an output to the comparator; the comparator comprises a digital circuit; the detector system further comprises a first voltage threshold coupled to an input of the comparator, the output of the comparator being used to analyze the response of the pixels in the pixel array; the detector array further comprises a multiplexer for multiplexing the output of the pixels and the test signal, the output of the multiplexer being coupled to the amplifier; the readout integrated circuit performs control of the stimulus source; the readout integrated circuit is external to the detector array; the readout integrated circuit controls the stimulus source to send photons towards the pixels in the pixel array at selected times; and / or the alert includes a fault indicator of the ASIL.

[0009] In another aspect, a detector system includes a stimulus source for transmitting photons toward pixels in a pixel array included in the detector system, a first module for analyzing a response of the pixels in the pixel array, and a second module for generating an alert based on the response of the pixels in the pixel array.

[0010] The system may further include one or more of the following features: the stimulus source includes a metal object that can be heated; the stimulus source includes a current source; the stimulus source includes a PN junction that provides a light emitting diode (LED); the first module is configured to analyze a response of a pixel in the pixel array by determining that no response is generated for a predetermined time period corresponding to a predetermined distance; an alert is generated based on the response of the pixel in the pixel array by determining that no response is generated for a predetermined time period corresponding to the predetermined distance; the first module analyzes the response of a pixel in the pixel array by determining that no response is generated for a predetermined time period corresponding to the predetermined distance after the stimulus source is controlled to send photons toward the pixel in the pixel array to stimulate the pixel to generate a response. the detector system comprises a photodiode coupled to an amplifier that provides an output to the comparator; the comparator comprises digital circuitry; the detector system further comprises a first voltage threshold coupled to an input of the comparator, the output of the comparator being used to analyze the response of the pixels in the pixel array; the detector array further comprises a multiplexer for multiplexing the output of the pixels and the test signal, the output of the multiplexer being coupled to the amplifier; the readout integrated circuit is configured to control the stimulus source; the readout integrated circuit is external to the detector array; the readout integrated circuit controls the stimulus source to send photons towards the pixels in the pixel array at selected times; and / or the alert includes a fault indicator of the ASIL.

[0011] In a further aspect, a method includes receiving a returning laser pulse at a detector system having pixels in a pixel array; analyzing a response of the pixels in the pixel array including comparing the response to at least one threshold corresponding to attenuation of optical energy of the laser pulse over distance and target reflectivity; and generating an alert signal based on the response of the pixels in the pixel array.

[0012] The method may further include one or more of the following features: the readout integrated circuit controls a laser that generates return laser pulses; the at least one threshold includes a first threshold corresponding to a first reflectivity and a second threshold corresponding to a second reflectivity; the step of analyzing the response includes determining that an actual return for the laser pulse corresponds to a response of a pixel in the pixel array that is between the first and second thresholds; the step of analyzing the response includes determining that noise corresponds to a response of a pixel in the pixel array that is below the second threshold; the step of analyzing the response includes determining that noise corresponds to a response of a pixel in the pixel array that is above the first threshold; the at least one threshold corresponds to a low trigger for a pulse generated by the first type of laser. the first time corresponds to a laser type including a fiber laser; and a second time corresponds to a laser type including a DPSS laser; determining a first time from when the return laser pulse exceeds the first threshold to when the return laser pulse exceeds the second threshold; determining, based on the first time, that the return laser pulse is generated by a second type of laser different from the first type of laser; determining, based on a pulse width of the return laser pulse, that the return laser pulse is generated by a second type of laser different from the first type of laser; the first time corresponds to a laser type including a fiber laser; and / or the first time corresponds to a laser type including a DPSS laser.

[0013] In a further aspect, the detector system comprises a detector for receiving a returning laser pulse, the detector comprising pixels in a pixel array; a first module configured to analyze a response of the pixels in the pixel array including comparing the response to at least one threshold corresponding to attenuation of optical energy of the laser pulse over distance and target reflectivity; and an alert signal configured to generate an alert based on the response of the pixels in the pixel array.

[0014] The system may further include one or more of the following features: the readout integrated circuit is configured to control a laser generating a return laser pulse; the at least one threshold includes a first threshold corresponding to a first reflectivity and a second threshold corresponding to a second reflectivity; the step of analyzing the response includes determining that an actual return for the laser pulse corresponds to a response of a pixel in the pixel array that is between the first and second thresholds; the step of analyzing the response includes determining that noise corresponds to a response of a pixel in the pixel array that is below the second threshold; the step of analyzing the response includes determining that noise corresponds to a response of a pixel in the pixel array that is above the first threshold; the at least one threshold includes a first threshold corresponding to a low trigger for a pulse generated by a first type of laser and a second threshold corresponding to a low trigger for a pulse generated by a first type of laser. and a second threshold corresponding to a high trigger for a pulse generated by the return laser pulse; the system is further configured to determine a first time from when the return laser pulse crosses the first threshold to when the return laser pulse crosses the second threshold; the system is further configured to determine, based on the first time, that the return laser pulse was generated by a second type of laser different from the first type of laser; the system is further configured to determine, based on a pulse width of the return laser pulse, that the return laser pulse was generated by a second type of laser different from the first type of laser; the first time corresponds to a laser type that includes a fiber laser; and / or the first time corresponds to a laser type that includes a DPSS laser.

[0015] In another aspect, a method includes using an amplifier to amplify a signal from a photodetector forming part of a detector system having a pixel array, applying an AC modulated signal to the amplifier, where an output signal of the amplifier includes a pulsed signal generated by a pixel in the pixel array included in the detector system and the AC modulated signal, analyzing the output signal from the amplifier to detect a fault in operation of the photodetector, and filtering the AC modulated signal from the output signal of the amplifier. The method may further include one or more of the following features: evaluating operation of the photodetector; and / or generating an alert based on the evaluation of the photodetector.

[0016] The foregoing features of the present disclosure, as well as the disclosure itself, can be more fully understood from the following description of the drawings. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a high-level block diagram of an exemplary detection system with safety features. [Figure 2] FIG. 2 is a schematic diagram of a portion of a pixel in a pixel array with pixel stimulation. [Figure 3] FIG. 1 is a schematic diagram of an exemplary circuit and operation of a pixel response and signal timeout. [Figure 3A] FIG. 10 is an exemplary circuit diagram for pixel response and signal timeout with current source stimulation. [Figure 3B] FIG. 3B is an exemplary block diagram for the circuit of FIG. 3A. [Figure 4] FIG. 10 is a diagram of voltage thresholds for optical energy return waveforms and reflectance values. [Figure 4A] FIG. 5 illustrates an exemplary circuit implementation for distinguishing actual signal returns using the reflectance values ​​of FIG. 4. [Figure 4B] FIG. 5 illustrates an exemplary circuit implementation for generating the voltage thresholds of FIG. 4. [Figure 5]FIG. 10 is a waveform diagram showing laser pulse characteristics for various laser types that can be used to verify the signal. [Figure 6] FIG. 6 illustrates an exemplary circuit implementation of dynamic photodetector bias modulation. [Figure 6A] FIG. 2 is a diagram illustrating an example of a modulated signal. [Figure 6B] FIG. 2 is a diagram illustrating an example of an optical signal. [Figure 7] FIG. 1 is a schematic diagram of an example computer capable of performing at least some of the processes described herein. DETAILED DESCRIPTION OF THE INVENTION

[0018] Before describing exemplary embodiments of the present disclosure, some information is provided. Laser ranging systems can include laser radar (ladar), light-detection and ranging (lidar), and distance measurement systems, which are generic terms for a class of devices that use light to measure distance to objects in a scene. The concept is similar to radar, except that optical signals are used rather than radio waves. Like radar, laser ranging imaging systems emit optical signals, e.g., pulsed or continuous optical signals, toward a specific location and measure the returning echo to estimate distance.

[0019] Laser ranging systems generally work by emitting a laser pulse and recording the time it takes for the laser pulse to travel to the target, reflect, and return to a receiver. The laser ranging device records the time of the outgoing pulse, either by triggering or by calculation using measurements of scattering from the outgoing laser light, and then records the time of the laser pulse's return. The difference between these two times is the flight time to the target and back. Using the speed of light, the round trip time of the pulse is used to calculate the distance to the target.

[0020] Lidar systems scan a beam over a target area to measure distances to multiple points across a field of view, generating a complete three-dimensional distance profile of the surroundings. For example, more advanced flash lidar cameras contain an array of detector elements, each capable of recording the time of flight to objects within their field of view.

[0021] When creating an image using optical pulses, the emitted pulse may capture multiple objects at various orientations as it traverses a 3D volume of space. The echoed laser pulse waveform contains a temporal and amplitude imprint of the scene. By sampling the optical echoes, a record of the interaction between the emitted pulse and captured objects in the scene is extracted, creating an accurate multidimensional image. To simplify signal processing and reduce data storage, laser ranging and imaging can be allocated to discrete return systems, which record only the time of flight (TOF) of the first or a few individual target returns to obtain an angle-angle-range image. In discrete return systems, each recorded return essentially corresponds to an individual laser reflection (i.e., an echo from one specific reflective surface, such as a vehicle, person, tree, pole, or building). Discrete return systems simplify signal processing and reduce data storage by recording only a few individual distances, but do so at the cost of loss of target and scene reflectivity data. Because laser pulse energy carries significant associated costs and increases the size and weight of the system, recording the TOF and pulse amplitude of multiple laser pulse return beams per transmitted pulse to acquire angle-angle-distance-intensity images increases the amount of information acquired per unit of pulse energy. All other things being equal, acquiring the full pulse return waveform offers a significant advantage, since maximum data is extracted from the average laser power input. In full-waveform systems, each backscattered laser pulse received by the system is digitized at a high sampling rate (e.g., 500 MHz to 1.5 GHz). This process generates a digitized waveform (amplitude versus time) that can be processed to achieve higher-fidelity 3D images.

[0022] Of the various laser ranging instruments available, those with a single-element receiver generally acquire distance data along a single distance vector at a fixed pointing angle. This type of instrument (commonly used by golfers and hunters, for example) acquires the distance (R) to one or more targets along a single pointing angle, or the distance and reflected pulse intensity (I) of one or more objects along a single pointing angle, resulting in pulse distance-intensity data (R,I). i where i denotes the number of pulse returns captured for each outgoing laser pulse.

[0023] More generally, laser ranging instruments can collect ranging data over a portion of a solid angle of a sphere subtended by two angular coordinates (e.g., azimuth and elevation), and this data can be calibrated to a grid of three-dimensional (3D) Cartesian coordinates. These systems are commonly referred to as 3D lidar and radar instruments. The terms "lidar" and "raider" are often used interchangeably, and for the purposes of this discussion, we will use the terms "3D lidar," "scanning lidar," or "lidar" to refer to these systems without loss of generality.

[0024] 3D lidar instruments acquire a three-dimensional (e.g., angle, angle, distance) data set. Conceptually, this is equivalent to using a rangefinder to scan across a scene and obtain the distance of objects in the scene to create a multi-dimensional image. When only distance is obtained from the returning laser pulse, these instruments can obtain a three-dimensional (e.g., angle, angle, distance) data set. n where the subscript n is used to reflect that we can collect a series of distance-resolved laser pulse return beams, not just the first reflection.

[0025] Some 3D lidar instruments are also capable of collecting the intensity of reflected pulse returns generated by objects located at resolved (angle, angle, range) objects in the scene. When both distance and intensity are recorded, a multidimensional data set [e.g., angle, angle, (distance-intensity)] is created. n ] is acquired. This is similar to a video camera, where for each instantaneous field of view (FOV), each active camera pixel acquires both the color and intensity of the scene observed through the lens. However, a 3D lidar system instead acquires the distance to the object and the intensity of the reflected pulse.

[0026] Lidar systems can include various types of lasers, including those operating at multiple different wavelengths, including invisible lasers (e.g., those operating at 840 nm or 905 nm wavelengths), near-infrared lasers (e.g., those operating at 1064 nm or 1550 nm), and thermal infrared lasers, including those operating in what is known as the "eye-safe" spectral region (i.e., generally above approximately 1400 nm). Lidar transmitters are generally invisible to the human eye. However, when the laser's wavelength approaches the human eye's sensitivity range (approximately 350 nm to 730 nm), the energy of the laser pulse and / or the average power of the laser must be reduced so that the laser operates at a wavelength insensitive to the human eye. Thus, for example, a laser operating at 1550 nm can generally have a laser pulse energy 200 to 1,000,000 times greater than that of a laser operating at 840 nm or 905 nm without causing eye damage.

[0027] One challenge for lidar systems is detecting low-reflectivity objects at long range, which requires transmitting a laser pulse with enough energy so that the return signal reflected from the distant target is large enough for detection. To determine the minimum required laser transmit power, several factors must be considered. For example, the magnitude of the pulse return scattered from a diffuse object in a scene is proportional to the object's distance, and the intensity of the return pulse generally decreases as a function of 1 / R for small objects. 4 and for larger objects it corresponds to a distance according to 1 / R 2 However, for highly specular objects (i.e., objects that are not diffusely scattering), a collimated laser beam can be reflected directly with almost no attenuation. This means that if a laser pulse is transmitted and then reflected from a target 1 meter away, the entire energy (J) from the laser pulse can be reflected back to the receiver, but if a laser pulse is transmitted and then reflected from a target 333 meters away, the returning light will be only about 10 of the transmitted energy. 12 This means that it may have a weak pulse of energy.

[0028] In many lidar systems, highly sensitive photodetectors are used to increase system sensitivity, reducing the amount of laser pulse energy required to reach low-reflectivity targets at the longest required distances while maintaining eye-safe operation. Several variations of these detectors incorporate photodiodes and / or provide gain, such as avalanche photodiodes (APDs) and single-photon avalanche detectors (SPADs). These variations can be configured as single-element detectors, segmented detectors, linear detector arrays, or area detector arrays. The use of highly sensitive detectors, such as APDs and SPADs, reduces the amount of laser pulse energy required for long-range ranging to low-reflectivity targets. A technical challenge for these photodetectors is that they must also be able to handle a very large dynamic range of signal amplitudes.

[0029] As dictated by the optical system's properties, the focal point of the laser return varies with distance. As a result, nearby objects often fall out of focus. Furthermore, also dictated by the optical system's properties, the location and size of the "blur"—i.e., the spatial extent of the optical signal—varies with distance, as with a standard camera. These challenges are typically addressed by using large, segmented, or multi-element detectors to capture all or only a portion of the light across the entire range of object distances. It is generally prudent to design the optical system so that reflections from nearby objects are blurred, so that a portion of the optical energy does not reach the detector or is spread among multiple detectors. This design strategy reduces the dynamic range requirements of the detector and prevents damage to the detector.

[0030] Acquiring a lidar image can involve a 3D lidar system embedded in the front of a vehicle, for example. The 3D lidar system includes a laser transmitter with any necessary optics, a single-element receiver with any necessary dedicated or shared optics, and an optical scanner used to scan ("paint") the laser across the scene. Here, generating a full-frame 3D lidar range image with a 20-degree by 60-degree field of view and an angular resolution of 0.1 degrees (10 samples per degree) requires the emission of 120,000 pulses [(20 × 10 × 60 × 10) = 120,000]. For example, given the 30-frame-per-second update rate required for automotive lidar, approximately 3.6 million pulses must be generated and their return light acquired per second.

[0031] There are many ways to combine and configure the elements of a lidar system, including considerations of laser pulse energy, beam divergence, detector array size and array format (single element, linear, 2D array), and the scanner used to acquire the 3D image. When a more powerful laser is used, a pixelated detector array can be used, in which case the laser divergence maps to a field of view wider than the detector array's field of view, requiring a proportionally increased laser pulse energy to accommodate the larger field of view. For example, compared to the 3D lidar described above, a 120,000-element (e.g., 200 × 600 element) detector array can be used with a laser having 120,000 times the pulse energy to acquire the same resolution 30 times per second. The advantage of this "flash lidar" system is that it does not require an optical scanner. The disadvantages are that a larger laser results in a larger, heavier system that consumes more power, and the laser's required higher pulse energy may potentially cause eye damage. The maximum average laser power and maximum pulse energy are limited by the requirement that the system be eye-safe.

[0032] As noted above, while many lidar systems operate by recording only the laser's time of flight and using that data to obtain the distance to the (closest) target of the first target return, some lidar systems are capable of obtaining both the distance and intensity of one or more target returns generated from each laser pulse. For example, in a lidar system capable of recording multiple laser pulse returns, the system can detect and record the distance and intensity of multiple returns from a single transmitted pulse. Such multipulse lidar systems can record the distance and intensity of a return pulse from a nearby object, as well as the distance and intensity of that pulse's subsequent reflection (after passing the nearby object and reflecting off a more distant object). Similarly, if sun glare or another laser pulse reflected from dust in the air is detected and erroneously recorded, the multipulse lidar system can still obtain the return from the actual target in its field of view.

[0033] The amplitude of the pulse return depends primarily on the target's specular and diffuse reflectance, its size, and its orientation. Laser returns from nearby, highly reflective objects are orders of magnitude greater than those from distant targets. Many lidar systems require highly sensitive photodetectors, such as avalanche photodiodes (APDs), which, along with their CMOS amplifier circuitry, allow detection of targets with low reflectivity, assuming the receiver components are optimized for high conversion gain. These detectors can be damaged by very intense laser pulse returns, primarily due to their high sensitivity.

[0034] However, acquiring pulse intensities over the larger dynamic range associated with laser ranging can be difficult because the signals are too large to acquire directly. Intensity can be inferred using recording of the bit-modulated output obtained using serial bit encoding from one or more voltage threshold levels. This technique is often called time-over-threshold (TOT) recording, or multiple-time-over-threshold (MTOT) recording when multiple thresholds are used.

[0035] 1 illustrates an exemplary detector system 100 with safety features. A detector array 102, which may comprise a focal plane array (FPA) 105 having a pixel array, is coupled to a readout module 104, such as a readout integrated circuit (ROIC). While the FPA 105 is shown as an ROIC and detector array in another embodiment, they may also be comprised of a single material element, for example, a silicon FPA. Furthermore, the readout module 106 may comprise silicon circuitry, and the detector module 102 may include a different material, such as, but not limited to, GaAs, InGaAs, InGaAsP, and / or other detector materials.

[0036] In some embodiments, the detector array 102 can comprise a single pixel or a one-dimensional (1D), two-dimensional (2D), and / or three-dimensional (3D) array of pixels. The interface module 106 can output information from the readout module 104. The safety module 108 can analyze the operation of the detector system 100 and generate an alert upon detecting one or more faults. In some embodiments, the safety module 108 can provide Automotive Safety Integrity Level (ASIL) related functionality, as described in more detail below. The detector system 100 can include a regulator 110 to provide one or more regulated voltages for the system.

[0037] 2 shows a portion of a detector array 200 having a series of pixels 202 in proximity to a direct photon injection mechanism. Direct photon injection refers to generating optical energy near one or more pixels 202 to stimulate an optical response from the detector array 200. By stimulating a known response, the entire signal path of the detector system can be verified.

[0038] In one embodiment, the conductive trace 204 can be heated to a temperature that emits photons. The conductive trace 204 can be a trace on the detector array or a wire placed in proximity to the detector array within the package. The conductive trace can be a conductor, for example, a metal, including but not limited to, aluminum, copper, tungsten, or a material such as indium tin oxide. For example, the conductive trace 204 can be heated in a controlled manner, such as by applying a known current to the conductive trace 204 or wire and timing it to emit photons in a specific manner that results in a desired response from the detector array. If the desired response is not detected, a fault can be detected.

[0039] Although shown aligned with the center of pixel 202 in the illustrated embodiment, conductive trace 204 can be placed in any practical location with respect to at least one pixel to meet the needs of a particular application. Additionally, the geometry of conductive trace 204, such as thickness, length, height, and shape, can vary. In some embodiments, the cross section of conductive trace 204 can be cylindrical, like a wire, or rectangular or trapezoidal, as done in semiconductor metallization processes.

[0040] In another embodiment, a PN junction 206 can be formed near the pixel 202 to provide a photon-emitting light emitting diode (LED) 208. The PN junction 206 can be stimulated to emit photons in a particular manner that results in a desired response from the detector array. If the desired response is not detected, a fault may have occurred.

[0041] The PN junction 206 may be formed from any suitable material, such as silicon and non-silicon materials. In one embodiment, the PN junction comprises GaAs, InGaAs, or InGaAsP.

[0042] The stimulus source can be external to the detector array and ROIC (focal plane array), which provides controls for synchronizing the timing and also controls the amount of optical stimulation. This stimulus can be contained within the package in which the ROIC and APD, an example of a focal plane array (FPA), reside. In one embodiment, the stimulus can comprise an external LED diode of any size or shape, as long as the package placement and additional design provides the desired level of optical energy to stimulate the pixels 202. In one embodiment, the ROIC can provide a signal to a lidar system laser in a lidar system to pulse or apply a known signal at predetermined times.

[0043] This stimulus may interfere with the desired light signal, and therefore, the stimulus may be timed in one of the following ways, including but not limited to: 1) triggered in response to an external stimulus indicating a desired self-check to be performed, 2) triggered at device startup to ensure proper functioning each time power is applied, or 3) triggered after a period of time or timeout after receiving actual light return, allowing testing after each pulse (continuous test mode).

[0044] In other embodiments, a current source 210 can be used in place of the pixel response to simulate the response, or multiplexed 212. In this way, the signal path can be stimulated and verified. In some embodiments, an emissive pixel 202 may be used in place of a current source, either by replacing the live pixel or by multiplexing between the pixel's cathode or anode. In another embodiment, the emissive pixel can be on a readout circuit and, when stimulated, send light toward a detector array in a focal plane array. In some cases, this may require thinning the detector array. A separate emissive die may be located separately from the detector array or readout circuit die. This three-die solution is not shown.

[0045] FIG. 3 illustrates a portion of a detector system 300, such as the system of FIG. 1, which may form part of or be coupled to an ROIC. It should be understood that the detector system 300 may comprise a single pixel. A photodiode 302 is coupled to a bias voltage 304, e.g., 60 V. In the illustrated embodiment, a transimpedance amplifier (TIA) 306 is coupled to the cathode of the photodiode 302 and generates an output 308 that is provided to an input of a comparator 310. A threshold voltage Vth provides a second input to the comparator 310, which generates a threshold output signal 312. It should be understood that the TIA represents a current-to-voltage converter that can amplify the current from the photodiode 302. An alert module 314 can generate alerts to indicate one or more fault conditions.

[0046] In some embodiments, the detector system can provide an alert at a specified maximum distance to indicate that no response was received within a particular ranging range. In some embodiments, normal operation is not to generate an alert when a pulse is received and detected. This is therefore an "active" indicator of a non-responsive condition. This can be used in situations where there is a known obstruction, either simulated via a fiber delay loop or present in reality, and no response within that time interval indicates a problem with the system.

[0047] In the illustrated embodiment, the output of the amplifier 308 generates a pulse 320 generated by a current from the photodiode 304 in response to photon detection. The pulse 320 has an amplitude that exceeds a voltage threshold Vth at the input of the comparator 310. Within some maximum time window 322 corresponding to a maximum distance, the comparator output 312 should change state. If the comparator output 312 does not transition, an alert can be generated by the alert module 314. The trigger may correspond to the absence of a response within a set time 324 or window.

[0048] To verify detection operation, the pixel can be operated, or there can be a light stimulus generated by a heating element, LED, current source, etc., to determine whether the pixel circuitry will alert when a fault occurs. In the illustrated embodiment, a test pulse 326 can be generated to test the operation and alerting of the circuitry. For example, if there is an expectation that a "hit" should occur before a certain distance, then the absence of a transition of the timeout signal, e.g., comparator output 312, indicates a malfunction. In some embodiments, any practical timeout can be set to meet the requirements of a particular application.

[0049] 3A shows an example circuit implementation similar to circuit 300 of FIG. 3 with the addition of a multiplexer 340 having a first input from a photodiode 302 and a second input from a current source 342. The input selected by multiplexer 340 may be provided to amplifier 306. As described above, stimuli may be generated by current source 342 to assess circuit operation and alert generation.

[0050] FIG. 3B shows an example block diagram of a photodetector circuit 350 that receives input from a stimulus module 352, which may include a current source, and generates an output to a threshold detector module 354. For example, the stimulus module 352 may generate the test pulse 326 in FIG. 3. The threshold detector module 354 may verify operation of the circuit in response to a selected stimulus. For example, as described above, the threshold detector module 354 may evaluate a signal against one or more thresholds. The ROIC may include an external output signal 356 that may provide an alert. In some embodiments, the output signal 356 may include one or more ASIL signals that may be coupled to a remote system, such as an engine control unit (ECU), an obstacle detection controller, a vehicle control unit, a vehicle control system, or a vehicle computer.

[0051] 4 illustrates a detection system that includes features for reducing false positives. A first curve 400 shows amplitude over time for a given target at 90% reflectivity, and a second curve 402 shows amplitude over time for 10% reflectivity. The first curve 400 corresponds to a first voltage threshold Vth1, and the second curve 402 corresponds to a second voltage threshold Vth2.

[0052] In an exemplary embodiment, voltage pulses 410, 412 between a first voltage threshold Vth1 and a second voltage threshold Vth2 are generated by returning light, which is likely to be real. A voltage pulse 414 below the second voltage threshold Vth2 is likely to be noise. A voltage pulse 416 above the first voltage threshold Vth1 is likely to be noise.

[0053] As can be seen, the relationship between the attenuation of the returned optical energy and distance is modified by the reflectivity. The range of reflectivity can be selected based on the characteristics of the transmitted pulse, the expected target characteristics, the expected distance, etc. The detector can be calibrated using an actual light source, and the response energy can be modeled over time to provide a reasonable response range. This improves safety by enhancing the rejection of false pulses. Additionally, real pulses can be better distinguished.

[0054] FIG. 4A shows an example circuit implementation 450 including a photodiode 452 providing an input to an amplifier 454, which generates an output coupled to the inputs of first and second comparators 456, 458. In the illustrated embodiment, a bias voltage 459 of 60 V is applied to the photodiode 452. It should be understood that any practical bias voltage level can be used. A first voltage threshold Vth1 is coupled to a second input of the first comparator 456, and a second voltage threshold Vth2 is coupled to a second input of the second comparator 458. The outputs of the first and second comparators 456, 458 are provided as inputs to an AND gate 460, which changes state when the output of the amplifier 454 is between the first and second voltage thresholds Vth1, Vth2, for example, according to the first and second curves 400, 402 of FIG. 4 .

[0055] FIG. 4B illustrates an exemplary embodiment in which the first voltage threshold Vth1 is generated by a high-speed digital-to-analog converter (DAC) or a DAC that sets up an attenuating RC circuit.

[0056] FIG. 5 shows an exemplary plot of a first laser pulse 500 generated by a first type of laser, such as a fiber laser, and a second laser pulse 550 generated by a second type of laser, such as a diode-pumped solid-state (DPSS) laser. The laser pulses 500, 550 each have a different pattern of energy release. The first pulse 500 is a shorter, sharper pulse at a set time, while the second pulse 550 is a longer / wider pulse with a shallower rise and steeper fall. The characteristics of the transmitted laser pulses 500, 550 can be used to improve detection of lower energy pulses and also reduce false detection of pulses that do not match the pulse characteristics.

[0057] A first laser pulse 500 can be compared to a low trigger threshold 502 and a high trigger threshold 504 to time the pulse duration, e.g., the time it crosses the thresholds 502, 504 (rising) to the time it crosses them (falling). Multiple pulses that do not coincide (within a margin for distance and pulse reflectivity) and / or do not meet certain ratio characteristics between durations can be rejected. Relatively low energy pulses can be detected. In some embodiments, thresholds similar to the thresholds Vth1 and Vth2 of FIG. 4 can be used for the high and low triggers shown in FIG. 5, and circuitry similar to that shown in FIG. 4A can be used to process the received pulses.

[0058] As can be seen, the DPSS laser pulse 550 has a leakage period before the laser fires, which can be timed relative to the durations for the high and low triggers and compared to each other.

[0059] For example, if a detector expects to receive a first type of pulse 500, it can filter out, e.g., reject as noise, a second type of pulse 502. In some embodiments, the detector can reject pulses that are not of the expected type. For example, in an automotive application, there may be many devices that transmit pulses of various types. By filtering pulses from other types of lasers by pulse shape, false detections can be reduced.

[0060] In some embodiments, the pulse characteristics can be evaluated, for example, by design where manufacturing characteristics are understood, or can be characterized unit by unit using offline characterization, or can be evaluated by using a fiber delay loop or a target with known reflectivity at a known distance.

[0061] FIG. 6 shows an example circuit implementation of a portion of a photodetector with bias modulation for detecting circuit malfunctions. The photodetector can be biased at two terminals: a common cathode (tied to the other cathode) at a higher external voltage, and an internal point at a lower voltage below a current measurement circuit such as a TIA. The lower bias point is modulated to generate a known signal at a known frequency. Some characteristics of the response are bias-based, such as "dark current," but also gain and other characteristics. By coupling to and measuring a signal at a known injection frequency, the health and function of the photodiode can be monitored by comparing the response at the known frequency to an expected response. Deviations from the response can be used to trigger a safety condition indicating that the photodetector is not operating properly.

[0062] In an exemplary embodiment, photodiode 600 has a cathode coupled to a bias voltage source 602 and an anode coupled to the input of an amplifier 604, such as a TIA. An AC modulator 606 is coupled to amplifier 604 such that the output of the amplifier is modulated by a signal from the modulator. A high-pass filter 614 can filter the modulated signal.

[0063] As can be seen in FIG. 6A, the modulated signal from the output of amplifier 604 includes pulses 610 from photodiode 600 and a modulated signal amplitude 612 that matches the desired output generated by the AC modulated signal from modulator 606. The modulated signal at the output of amplifier 604 indicates proper operation of the circuit. As shown in FIG. 6B, a light output may be generated after high-pass filter 614 (set above the modulation frequency) filters the amplifier output to remove the modulated signal. This configuration allows the functionality of photodiode 600 to be checked. A signal comparison / evaluation module 613 can compare the desired signal to the actual signal to detect faults and / or generate alerts.

[0064] In another embodiment, the signal from the bias voltage source 602 may be modulated by the photodiode 600. By detecting the pulse / amplitude of the modulated signal at the output of the amplifier 604, the operation of the photodiode 600 can be checked.

[0065] FIG. 7 illustrates an exemplary computer 700 or controller capable of performing at least a portion of the processes described herein. For example, the computer 700 may execute a mask controller, such as the selection module 214 of FIG. 2, and processes to implement the steps in FIG. 5. The computer 700 includes a processor 702, volatile memory 704, non-volatile memory 706 (e.g., a hard disk or other memory such as flash, EEPROM, or RAM), an output device 707 and an audio control unit, and / or a graphical user interface (GUI) 708 (e.g., a mouse, keyboard, display, etc.). The non-volatile memory 706 stores computer instructions 712, an operating system 716, and data 718. In one example, the computer instructions 712 are executed by the processor 702 from the volatile memory 704. In one embodiment, an article 720 comprises non-transitory computer-readable instructions.

[0066] The process may be implemented in hardware, software, or a combination of the two. The process may be implemented in a computer program running on a programmable computer / machine, each of which includes a processor, a storage medium, or other article of manufacture readable by the processor (including volatile and non-volatile memory and / or storage elements), at least one input device, and one or more output devices. The program code may be applied to data entered using the input device to perform processing and generate output information.

[0067] The system may execute, at least in part, processes by a computer program product (e.g., in a machine-readable storage device) for execution by or to control the operation of a data processing device (e.g., a programmable processor, a computer, or multiple computers). Each such program may be implemented in a high-level procedural or object-oriented programming language to communicate with a computer system. However, the program may also be implemented in assembly or machine language. The language may be a compiled or interpreted language and may be deployed in any form, for example, as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program may be deployed to run on one computer, or on multiple computers at one site, or distributed across multiple sites and interconnected by a communications network. The computer program may be stored on a general-purpose or special-purpose programmable computer-readable storage medium or device (e.g., RAM / ROM including flash memory, or EEPROM, CD-ROM, hard disk, or magnetic diskette) and configures and operates the computer when the storage medium or device is read by the computer.

[0068] The process may also be implemented as a machine-readable storage medium configured to contain a computer program, the instructions of which, when executed, cause a computer to operate.

[0069] Processing may be performed by one or more programmable processors executing one or more computer programs to perform the functions of the system. All or part of the system may be implemented as special purpose logic circuitry (e.g., an FPGA (field programmable gate array), a general purpose graphics processing unit (GPGPU), and / or an ASIC (application-specific integrated circuit)).

[0070] While exemplary embodiments of the present disclosure have been described, it will now be apparent to those skilled in the art that other embodiments incorporating these concepts may also be used. The embodiments contained herein should not be limited to the disclosed embodiments, but rather should be limited only by the spirit and scope of the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.

[0071] Elements of various embodiments described herein may be combined to form other embodiments not specifically described above. Various elements described in the context of a single embodiment may be provided separately or in any suitable subcombination. Other embodiments not specifically described herein are also within the scope of the appended claims.

Claims

1. receiving the returning laser pulses with a detector system including a detector having pixels in a pixel array and a stimulation source; analyzing the response, including comparing the detector response to the returning laser pulse with at least one threshold corresponding to attenuation of optical energy of the laser pulse over distance and target reflectivity; generating an alert signal based on a response output from the detector in response to an optical or electrical stimulus applied to the detector from the stimulus source; A method comprising:

2. The method of claim 1 , wherein a readout integrated circuit controls a laser that generates the return laser pulses.

3. The method of claim 1 , wherein the at least one threshold comprises a first threshold corresponding to a first reflectance and a second threshold corresponding to a second reflectance.

4. 4. The method of claim 3, wherein analyzing the response includes determining that an actual return for the laser pulse corresponds to the response of the detector that is between the first threshold and the second threshold.

5. The method of claim 4 , wherein analyzing the response includes determining that noise corresponds to the response of the detector being below the second threshold.

6. The method of claim 5 , wherein analyzing the response includes determining that noise corresponds to the response of the detector exceeding the first threshold.

7. 2. The method of claim 1, wherein the at least one threshold comprises a first threshold corresponding to a low trigger for pulses generated by a first type of laser and a second threshold corresponding to a high trigger for the pulses generated by the first type of laser.

8. The method of claim 7 , further comprising determining a first time from when the return laser pulse exceeds the first threshold to when the return laser pulse exceeds the second threshold.

9. The method of claim 8 , further comprising determining, based on the first time, that the return laser pulse was generated by a second type of laser that is different from the first type of laser.

10. 10. The method of claim 9, further comprising determining, based on a pulse width of the return laser pulse, that the return laser pulse was generated by a second type of laser different from the first type of laser.

11. The method of claim 8 , wherein the first time corresponds to a laser type that includes a fiber laser.

12. The method of claim 8 , wherein the first time corresponds to a laser type that includes a DPSS laser.

13. a detector for receiving returning laser pulses, the detector comprising pixels in a pixel array; a first module configured to analyze the response, including comparing the detector response to the returning laser pulse with at least one threshold corresponding to attenuation of optical energy of the laser pulse over distance and target reflectivity; a stimulus source configured to apply an optical or electrical stimulus to the detector; an alert module configured to generate an alert based on a response output from the detector in response to the optical stimulus or the electrical stimulus; A detector system comprising:

14. The system of claim 13 , wherein a readout integrated circuit is configured to control a laser that generates the return laser pulses.

15. The system of claim 13 , wherein the at least one threshold comprises a first threshold corresponding to a first reflectance and a second threshold corresponding to a second reflectance.

16. 16. The system of claim 15, wherein analyzing the response includes determining that an actual return for the laser pulse corresponds to the response of the detector that is between the first threshold and the second threshold.

17. 17. The system of claim 16, wherein analyzing the response includes determining that noise corresponds to the response of the pixel of the detector being below the second threshold.

18. The system of claim 17 , wherein analyzing the response includes determining that noise corresponds to the response of the detector exceeding the first threshold.

19. 14. The system of claim 13, wherein the at least one threshold comprises a first threshold corresponding to a low trigger for pulses generated by a first type of laser and a second threshold corresponding to a high trigger for the pulses generated by the first type of laser.

20. 20. The system of claim 19, further configured to determine a first time from when the return laser pulse exceeds the first threshold to when the return laser pulse exceeds the second threshold.

21. 21. The system of claim 20, further configured to determine, based on the first time, that the return laser pulse was generated by a second type of laser that is different from the first type of laser.

22. 22. The system of claim 21, further configured to determine, based on a pulse width of the return laser pulse, that the return laser pulse was generated by a second type of laser different from the first type of laser.

23. 21. The system of claim 20, wherein the first time corresponds to a laser type that includes a fiber laser.

24. 21. The system of claim 20, wherein the first time corresponds to a laser type comprising a DPSS laser.

25. using an amplifier to amplify a signal from a photodetector forming part of a detector system having a pixel array; applying an AC modulated signal to the amplifier, wherein an output signal of the amplifier comprises a pulse signal generated by a pixel in a pixel array included in a detector system and the AC modulated signal; filtering the AC modulated signal from the output signal of the amplifier; applying an optical stimulus to the photodetector or an electrical stimulus to the amplifier by a stimulus source forming part of the detector system; analyzing a signal output from the photodetector or the amplifier in response to application of the optical stimulus or the electrical stimulus to detect a disturbance in the operation of the photodetector or the amplifier; A method comprising:

26. 26. The method of claim 25, further comprising evaluating said operation of said photodetector.

27. 27. The method of claim 26, further comprising generating an alert based on the evaluation of the optical detector.

Images