Patent Application
20220091239
In various examples, aspects of the present disclosure are directed to detecting the position of objects in target areas by use of a receiver with single-photon avalanche photodiode (SPAD) technology.
SPAD technology, as well as the related field of Lidar (light detection and ranging), play increasingly important roles in many technology areas. One such area is in the field of range detection as may be applied for sensing the relative movement of objects. In vehicular applications, this type of detection may be used for providing assistance in connection with both non-autonomous driving and, due to high range and angular resolutions, autonomous driving. SPAD is an advantageous receiver technology for automotive Lidar thanks to its unique properties such as high sensitivity down to a single photon, high time resolution and high array resolution which may be enabled by planar device structure (e.g., CMOS-based SPAD).
SPAD also facilitates effective techniques for time-of-flight measurements for short-range and low-noise environment applications, such as fluorescence lifetime microscopy. Adapting SPAD for a long-range and/or high noise environment, in addition to optical bandpass filter and limited field-of-view, requires comprehensive range-gating technique due to the blocking of the signal by noise-induced detections, for example, sunlight photons. In such environments with constant photon arrival rates, for example, the probability of photon detection drops exponentially with the time, referred to as pile-up effect.
A SPAD based receiver has the potential to form a large array, achieving a wide field of view (FoV) with high image resolution. In a photon-starved application, for example, scaling does not increase the photon counts proportionally. Thus, SPAD events share timestamping resources in the interest of silicon area reduction. In contrast, high ambient noise condition enforces fully parallel architecture to maximize photon detections. Consequently, throughput and power consumption increase proportional to the activity rate.
These and other matters have presented challenges to efficiencies of realizing effective use of SPAD over longer ranges, with enhanced accuracy and/or in higher noise environments, for a variety of applications.
Various example embodiments are directed to issues such as those addressed above and/or others which may become apparent from the following disclosure concerning operation of a SPAD receiver such as may be used in a Lidar (Light Detection and Ranging) system.
In certain example embodiments, aspects of the present disclosure involve a SPAD receiver having circuitry for photon detection and having a plurality TDCs (time-to-digital converters) to detect multiple photons. Such circuitry may be set to provide relatively coarse timestamps of the detected photons, which are accumulated to construct a coarse-bin histogram. In such circuitry, bin accumulated photon (or in some instances avalanche triggering) counts may occur over relatively coarse times for the associated time ranges. Possible targets may then be identified by examination of the photon count distribution over the bins. Upon identification of the possible target(s), a plurality of TDCs may be used to accumulate detected photon counts over more fine time ranges (relative to the coarse mode) such as the time ranges corresponding to identified targets.
In more-specific related examples, in one frame TDCs may be gated within the target bins provided by an integrated coarse histogram. Such an integrated coarse histogram may be built with additional timestamping device (e.g., counters) running in the background. Further, separation and simultaneity of the coarse and fine histogramming may be used to reduce loss in total integration time, thereby reducing loss in terms of signal to noise ratio. Using such specific aspects, with slightly additional hardware (e.g., counter logic circuitry and coarse histogram memory), the TDCs may be gated within the target windows with appropriate operational numbers, thereby reducing or minimizing noise counts in fine-histogram construction. Alternatively, the least-significant bit (LSB) size of the TDCs may be changed at the cost of frame rates or integration time (or data acquisition time) of the fine resolution histogram construction due to the time consumed to generate the coarse target bins.
Another example involves operating a SPAD receiver for Lidar (Light Detection and Ranging) detection of at least one object that is among one or more possible target bins associated with binning and identification. This example may further include operating the SPAD receiver for a more refined Lidar detection of the at least one object while using the plurality of TDCs to detect possible targets.
Another specific example involves a method for accumulating detected photon counts in an array of bins in response to being detected. Also, such a method may involve operating the SPAD receiver for Lidar detection of at least one object in an environment that causes at least one of the bins in the array of bins to be associated with the at least one object. Similarly, at least one other of the bins, in the array of bins, may be associated with noise.
The above discussion/summary is not intended to describe each embodiment or every implementation of the present disclosure. The figures and detailed description that follow also exemplify various embodiments.
Various example embodiments may be more completely understood in consideration of the following detailed description in connection with the accompanying drawings, in which certain aspects may stand alone and/or also may relate to and be used in connection with other aspects. These accompanying drawings include:
While various embodiments discussed herein are amenable to modifications and alternative forms, aspects thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the disclosure to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure including aspects defined in the claims. In addition, the term “example” as used throughout this application is only by way of illustration, and not limitation.
Aspects of the present disclosure are believed to be applicable to a variety of different types of apparatuses, systems and methods involving the use of a SPAD (Single Photon Avalanche Diode) receiver system to characterize distances to a target and as well as a photon count to characterize signal-to-noise ratio (SNR) of the receiver signal. In certain implementations, aspects of the present disclosure have been shown to be beneficial when used in the context of distance ranging and signal strength determination. This may include areas such as robot navigation, perimeter security, or cartography. In some embodiments, such a SPAD receiver system may be beneficial in a Lidar (light detection and ranging) system such as implementations used on autonomous vehicles. As a specific example, such a system may be used to quantify 3D information about a target environment such as the roadway in front of a car, such as pedestrian locations, approaching vehicles, etc. While not necessarily so limited, various aspects may be appreciated through the following discussion of non-limiting examples which use such exemplary contexts.
Accordingly, in the following description various specific details are set forth to describe specific examples presented herein. It should be apparent to one skilled in the art, however, that one or more other examples and/or variations of these examples may be practiced without all the specific details given below. In other instances, well known features have not been described in detail so as not to obscure the description of the examples herein. For ease of illustration, the same reference numerals may be used in different diagrams to refer to the same elements or additional instances of the same element. Also, although aspects and features may in some cases be described in individual figures, it will be appreciated that features from one figure or embodiment can be combined with features of another figure or embodiment even though the combination is not explicitly shown or explicitly described as a combination.
According to a specific example of the present disclosure, embodiments are directed to or involve a method wherein a SPAD receiver may include a SPAD circuit used to detect incoming photons and using multiple photon detections while using, for example, a plurality of TDCs (time-to-digital converters). This exemplary approach may also involve accumulating (counting) detected photons over relatively coarse ranges. Accumulation (counting) of photons may be computed via a plurality of pixels. Such pixels may be within a pixel group (per pixel, row, per column, etc.). The accumulated photon may be binned according to the associated relative coarse time range. From such bins, one or more possible targets bins may be identified.
Also, as with the previous example, range information associated with detected target bin(s) may be used, and a plurality of TDCs may be used so as to accumulate detected photons over one or more relatively fine time ranges. Such ranges may correspond to the identified one or more target bins for accurate identification indications of the target object(s).
In other specific examples, the present disclosure is directed to a method, wherein operation of the SPAD receiver may be for Lidar (Light Detection and Ranging) detection of at least one object that is among the one or more possible target bins associated with the steps or activities of binning and identification as discussed in connection with other examples herein. Further, the SPAD receiver may be operated for more refined Lidar detection of the object(s) while using the TDCs and counting logic circuitry (or hardware) as also described herein.
In yet another specific example, the present disclosure concerns embodiments directed to or involving methodology for accumulating detected photons counts in an array of bins in response to being detected. Also, such methodology may involve operating the SPAD receiver for Lidar detection of at least one object in an environment that causes at least one of the bins in the array of bins to be associated with one or more of the target objects. Similarly, at least one other of the bins, among the array of bins, may be associated with noise (e.g., sunlight or interfering light from an unintended source). Note that the background noise may be measured by a SPAD array or auxiliary ambient light sensor and eth SPAD receiver may be calibrated, by way of threshold-detection settings in the logic processing, to ignore or discard such noise.
Turning now to the drawings,
Continuing with the description of
As another related feature which may be optionally used in connection with the example embodiments of the present disclosure, a plurality of separate blocks as in
An example implementation of an adaptive TDC range gating and target bin identification system is illustrated in
The example of
In this specific example and as further shown in connection with the integrated coarse histogram of
According to another specific example, the present disclosure concerns embodiments involving methods wherein binning and identifying one or more possible target bins, as associated with the detected photon counts accumulated over the relatively coarse time ranges, includes discarding or ignoring the other bin or bins in the array of bins which may be associated with noise such as sunlight.
In yet another specific example of the instant disclosure, embodiments are directed to or involve a method wherein the TDCs are used in order to accumulate detected photon counts, over one or more relatively fine time ranges, and this may include allocating the one or more relatively fine time ranges for a plurality of the TDCs. These ranges may be selectively based on the steps of binning and identifying one or more possible target bins. Further, the targets bins may be associated with the detected photon counts accumulated over the relatively coarse time ranges. The allocation among the TDCs, for relatively fine time ranges technique, may alleviate two multiple issues including, for example, limited time-stamping capability in a TDC sharing architecture; and/or high throughput in a per-pixel TDC architecture. The integrated coarse histogram-based data preselection may enable effective TDC allocation at the target bins. Thus, noise induced time-stamping may be reduced, hence throughput may be reduced and SNR may be retained.
In certain more specific examples, operating the SPAD receiver may include a plurality of TDCs with pixel groups covering a field of view. Such pixel groups may be coupled to a bank of the plurality of TDCs to mitigate or prevent a blind spot in the field of view.
Another more specific example is directed to a method involving storing data associated with the detected photon counts as accumulated over the relatively coarse time ranges, in a coarse histogram. Filtering the histogram data may also be used with this example to identify a possibly-changing bin among the one or more possible target bins.
Consistent with above aspects, yet other detailed examples involve a method of operating the SPAD receiver with a step that includes updating the coarse histogram in real time. This in real-time updating may be implemented to facilitate maintaining the system frame rate as detected photons are processed by the receiver's circuitry.
Another detailed example involves a method that includes using the SPAD receiver to detect jamming. As described previously, any coarse histogram bin reaching the theoretically maximum photon counts may be regarded as a jamming occurrence or situation.
Other specific examples, each relating and useful in combination with one or more of the above-discussed examples, are directed to ways in which bottlenecking in connection with the processing of the detected photons may be avoided. In one such example, the SPAD-based receiver includes circuitry configured for Lidar detection of at least one object (among one or more possible target bins associated with the binning and identification) and circuitry for more refined Lidar detection of the object or objects while using the plurality of TDCs and in response to the TDCs being used. In another such example, the receiver includes such Lidar detection circuitry and also memory circuitry to accumulate detected photon counts in an array of bins; the Lidar detection is to detect the object or objects in an environment that causes at least one of the bins in the array of bins to be associated with the at least one object and at least one other of the bins in the array to be associated with noise (such as extraneous light as may be caused by the sun or an artificial source). In other such examples, during operation of the receiver, the plurality of TDCs are used to accumulate detected photon counts over one or more relatively fine time ranges in order to allocate the one or more relatively fine time ranges for the plurality of TDCs, and/or the receiver includes data processing circuitry is to associate the plurality of TDCs with pixel groups covering a field of view, wherein each of the pixel groups is coupled to a bank of the plurality of TDCs to mitigate or prevent a blind spot in the field of view. In yet further related examples, the receiver includes logic circuitry to discriminate among the detected photons before using the plurality of TDCs to mitigate or prevent an overload of detected photons (e.g., due to sunlight) being processed by the receiver.
As examples, the Specification describes and/or illustrates aspects useful for implementing the claimed disclosure by way of various circuits or circuitry which may be illustrated as or using terms such as blocks, modules, device, system, unit, controller, and/or other circuit-type depictions (e.g., reference numerals 220 and 240 of
For example, in certain of the above-discussed embodiments, one or more modules are discrete logic circuits or programmable logic circuits configured and arranged for implementing these operations/activities, as may be carried out in the approaches shown in
Based upon the above discussion and illustrations, those skilled in the art will readily recognize that various modifications and changes may be made to the various embodiments without strictly following the exemplary embodiments and applications illustrated and described herein. For example, methods as exemplified in the Figures may involve steps carried out in various orders, with one or more aspects of the embodiments herein retained, or may involve fewer or more steps such as the steps/activities associated with
