Lidar Motion Correction via Phase Vector Components
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Solution Overview
Problem
Time-of-flight lidar systems face challenges in accurately determining the distance of moving targets due to phase vector changes between subframes, leading to potential misreadings, especially in high-speed applications like automotive scenarios.
Innovation Solution
The implementation of a circuit that calculates intermediate phase vectors from component measurements across subframes, allowing for the estimation of target velocity and correction of distance measurements for motion, using phase data from detector pixels and integration with image sensor data for dwell time determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional ToF measurement is used without motion correction, then the system is simple and fast, but measurement precision deteriorates for moving targets
Solution Approach 1:
The system performs preliminary velocity estimation using phase data from multiple subframes before final distance measurement. By calculating intermediate phase vectors and estimating target velocity in advance, the system compensates for motion effects during the measurement process, improving accuracy without requiring complex real-time correction mechanisms
Solution Approach 2:
The measurement process is divided into separate subframes, with each subframe capturing phase data at different time points. This segmentation allows the system to track phase changes over time, estimate velocity, and correct distance measurements for moving targets while maintaining overall system simplicity
2Measurement precision
If multiple subframes are used for velocity estimation, then measurement precision improves, but loss of time increases
Solution Approach 1:
The system uses a minimal number of subframes (typically 3-5) sufficient for velocity estimation rather than continuous sampling. This partial action approach provides adequate velocity information for motion correction while minimizing the time overhead compared to using excessive numbers of subframes
Solution Approach 2:
The system varies the time interval between subframes and the number of subframes used based on detected target motion characteristics. For slowly moving targets, fewer subframes with longer intervals are used, while faster targets trigger more frequent sampling, optimizing the balance between precision and time loss
3Reliability
If phase data from multiple subframes is processed, then reliability improves for moving targets, but device complexity increases
Solution Approach 1:
The system implements feedback by using detected target motion to adjust processing parameters. Velocity estimation from phase data feeds back into the distance measurement process, allowing dynamic correction for moving targets. This feedback mechanism improves reliability while keeping processing complexity manageable through adaptive rather than universally complex processing
Solution Approach 2:
Intermediate phase vectors serve as mediators between raw phase data and final distance measurements. These intermediate representations simplify the processing by providing a standardized form for velocity estimation, making the overall system more reliable and easier to process than directly handling raw multi-subframe phase data
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the accuracy of distance measurements for moving targets by accounting for velocity changes and dwell times, reducing errors associated with target motion and improving dynamic range in lidar systems.
Implementation Method 1
Time of flight (ToF) based imaging is used in a number of applications including range finding, depth profiling, and 3D imaging
Implementation Method 2
one or more light detector pixels (including one or more semiconductor photodetectors, such as photodiodes, including avalanche photodiodes and single-photon avalanche detectors; generally referred to herein as detector elements or detectors, which output detection signals in response to incident light)
Data Source
AI summary
A flash LIDAR apparatus includes emitter units configured to emit optical signals over a field of view, and detector pixels configured to output detection signals responsive to light representing the optical signals incident thereon. The detection signals correspond to respective phase offsets relative to a frequency of the optical signals. A circuit is configured to determine component measurements corresponding to the respective phase offsets from the detection signals, and calculate a distance of a target from which the light was reflected based on the detection signals. The distance is corrected for motion of the target based on subsets of the component measurements.