US-20260126530-A1 - PROCESSING TIME-SERIES MEASUREMENTS FOR LIDAR ACCURACY

US20260126530A1US 20260126530 A1US20260126530 A1US 20260126530A1US-20260126530-A1

Abstract

An optical measurement system may include a light source and corresponding photosensor configured to emit and detect photons reflected from objects in a surrounding environment for optical measurements. An initial peak can be identified as resulting from reflections off a housing of the optical measurement system. This peak can be removed or used to calibrate measurement calculations of the system. Peaks resulting from reflections off surrounding objects can be processed using on-chip filters to identify potential peaks, and the unfiltered data can be passed to an off-chip processor for distance calculations and other measurements. A spatial filtering technique may be used to combine values from histograms for spatially adjacent pixels in a pixel array. This combination can be used to increase the confidence for distance measurements.

Inventors

ANGUS PACALA
Marvin SHU

Assignees

Ouster, Inc.

Dates

Publication Date: 20260507
Application Date: 20251219

Claims (20)

1 . An optical measurement system comprising: a light source configured to transmit one or more pulse trains over one or more time intervals as part of an optical measurement, wherein each of the one or more time intervals includes one of the one or more pulse trains; a photosensor configured to detect photons from the one or more pulse trains that are reflected from an object in an environment surrounding the optical measurement system; a plurality of registers configured to accumulate photon counts from the photosensor received during the one or more time intervals to represent an unfiltered histogram of photon counts received during the one or more time intervals; a filter circuit configured to provide a filtered histogram of the photon counts from the plurality of registers; and a peak detection circuit configured to: detect a location of a peak in the filtered histogram, and identify, using the location of the peak in the filtered histogram, locations in the plurality of registers storing an unfiltered representation of the peak.
2 . The optical measurement system of claim 1 , further comprising a processor configured to receive the unfiltered representation of the peak and calculate a distance to the object in the environment surrounding the optical measurement system using the unfiltered representation of the peak.
3 . The optical measurement system of claim 1 , wherein the filter circuit is configured to provide the filtered histogram by applying a matched filter that corresponds to the one or more pulse trains.
4 . The optical measurement system of claim 1 , wherein a pulse train in the one or more pulse trains comprises a plurality of square pulses.
5 . The optical measurement system of claim 1 , wherein the filter circuit is configured to low-pass filter the unfiltered histogram.
6 . The optical measurement system of claim 1 , further comprising a second plurality of registers that stores the filtered histogram.
7 . The optical measurement system of claim 1 , wherein the filtered histogram is generated on a single pass through the plurality of registers.
8 . The optical measurement system of claim 7 , wherein the peak is detected during the single pass through the plurality of registers such that the filtered histogram is not stored in its entirety.
9 . The optical measurement system of claim 1 , wherein the peak detection circuit is configured to detect the location of the peak by detecting increasing values followed by decreasing values in the plurality of registers.
10 . The optical measurement system of claim 1 , wherein the processor is implemented on an integrated circuit (IC) that is separate and distinct from an IC on which the plurality of registers is implemented.
11 . The optical measurement system of claim 1 , wherein the light source and the photosensor form a pixel in a plurality of pixels in the optical measurement system.
12 . A method of analyzing filtered and unfiltered data in an optical measurement system, the method comprising: transmitting one or more pulse trains over one or more first time intervals as part of an optical measurement, wherein each of the one or more first time intervals includes one of the one or more pulse trains; detecting photons from the one or more pulse trains that are reflected off an object in an environment surrounding the optical measurement system; populating a plurality of registers using the photons to represent an unfiltered histogram of photon counts received during the one or more first time intervals; filtering the unfiltered histogram in the plurality of registers to provide a filtered histogram of the photons from the plurality of registers; detecting a location of a peak in the filtered histogram; identifying, using the location of the peak in the filtered histogram, locations in the plurality of registers storing an unfiltered representation of the peak; and sending the unfiltered representation of the peak to a processor to calculate a distance to the object in the environment surrounding the optical measurement system using the unfiltered representation of the peak.
13 . The method of claim 12 , wherein sending the unfiltered representation of the peak comprises sending information identifying histogram time bins represented in the plurality of registers that store the unfiltered representation of the peak.
14 . The method of claim 12 , wherein filtering the unfiltered histogram in the plurality of registers comprises applying convolving the unfiltered histogram with at least one square filter having a plurality of identical values.
15 . The method of claim 14 , wherein the plurality of identical values comprises a sequence of binary “1” values and/or a sequence of “−1” values.
16 . The method of claim 12 , wherein filtering the unfiltered histogram in the plurality of registers comprises convolving the unfiltered histogram with at least one sequence comprising a non-zero value followed by a plurality of zero values.
17 . The method of claim 16 , wherein the at least one sequence comprises a single binary “1” value or a single binary “−1” followed by a plurality of “0” values.
18 . The method of claim 12 , further comprising sending a filtered representation of the peak to the processor in addition to sending the unfiltered representation of the peak.
19 . The method of claim 12 , wherein: the location of the peak in the filtered histogram is detected as a single peak in the filtered histogram; and the unfiltered representation of the peak comprises at least two peaks in the unfiltered histogram.
20 . The method of claim 19 , wherein one of the at least two peaks in the unfiltered histogram represents a peak resulting from a reflection of the one or more pulse trains off a housing or window of the optical measurement system.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS This application is a continuation of U.S. Non-Provisional application Ser. No. 17/451,633, filed Oct. 20, 2021, entitled “PROCESSING TIME-SERIES MEASUREMENTS FOR LIDAR ACCURACY” which is a continuation of International Application No. PCT/US2020/055265 filed Oct. 12, 2020, entitled “PROCESSING TIME-SERIES MEASUREMENTS FOR LIDAR ACCURACY” which claims the benefit of U.S. Provisional Patent Application No. 62/913,604, filed on Oct. 10, 2019, entitled “PROCESSING TIME-SERIES MEASUREMENTS FOR LIDAR ACCURACY.” The disclosures of these applications are incorporated herein by reference. BACKGROUND Light Detection And Ranging (LIDAR) systems are used for object detection and ranging, e.g., for vehicles such as cars, trucks, boats, etc. LIDAR systems also have uses in mobile applications (e.g., for face recognition), home entertainment (e.g., to capture gesture capture for video game input), and augmented reality. A LIDAR system measures the distance to an object by irradiating a landscape with pulses from a laser, and then measuring the time for photons to travel to an object and return after reflection, as measured by a receiver of the LIDAR system. A detected signal is analyzed to detect the presence of reflected signal pulses among background light. A distance to an object can be determined based on a time-of-flight from transmission of a pulse to reception of a corresponding reflected pulse. It can be difficult to provide robust distance accuracy down to a few centimeters in all conditions, particularly at an economical cost for the LIDAR system. Promising new detector technologies, like single photon avalanche diodes (SPADs), are attractive but have significant drawbacks when used to measure time-of-flight and other signal characteristics due to their limited dynamic range, particularly over a broad range of ambient conditions and target distances. Additionally, because of their sensitivity to even a small number of photons, SPADs can be very susceptible to ambient levels of background noise light. BRIEF SUMMARY In some embodiments, an optical measurement system may include a housing of the optical measurement system and a light source configured to transmit one or more pulse trains over one or more time intervals as part of an optical measurement, where each of the one or more first time intervals may include one of the one or more pulse trains. The system may also include a photosensor configured to detect photons from the one or more pulse trains that are reflected off of a housing of the optical measurement system, and to detect photons from the one or more pulse trains that are reflected off of objects in an environment surrounding the optical measurement system. The system may additionally include a plurality of registers configured to accumulate photon counts from the photosensor received during the one or more time intervals. Each of the one or more time intervals may be subdivided into a plurality of time bins. Each of the plurality of registers may be configured to accumulate photon counts received during a corresponding one of the plurality of time bins in each of the one or more time intervals to represent a histogram of photon counts received during the one or more time intervals. The system may further include a circuit configured to identify an initial peak in the histogram of photon counts. The initial peak may represent the photons reflected from the housing of the optical measurement system. In any embodiments, any or all of the following features may be included in any combination and without limitation. The circuit may be configured to identify the initial peak by identifying a predetermined number of registers in the plurality of registers that occur first in the plurality of registers. The circuit may be configured to identify the initial peak by identifying one or more registers in the plurality of registers storing a highest number of photon counts. The circuit may be configured to identify the initial peak by identifying registers in the plurality of registers with time bins that correspond to a distance between the light source and the housing of the optical measurement system. The circuit may be further configured to identify a subset of the plurality of registers that represents the initial peak. The subset of the plurality of registers may be identified by selecting a predetermined number of registers around a register storing a maximum value of the initial peak. The subset of the plurality of registers may be identified by selecting registers around a register storing a maximum value of the initial peak that store values that are within a predetermined percentage of the maximum value. The circuit may be further configured to estimate a distance between the light source and the housing of the optical measurement system based on a location of the initial peak in the plurality of registers. The circuit may be further configured to calibrate d