FMCW LIDAR Sensor Distance Acquisition via Sub-Phase Segmentation
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Solution Overview
Problem
Current LIDAR FMCW-type sensors face challenges in accurately measuring distances for a large number of pixels simultaneously at high acquisition rates due to limitations in signal-to-noise ratio and noise increase with bandwidth expansion, leading to potential counting errors.
Innovation Solution
The method involves dividing the acquisition duration into multiple sub-phases with varying frequency excursion and duration, allowing for targeted distance measurement ranges within each sub-phase, reducing bandwidth and increasing signal-to-noise ratio by adjusting the ratio of frequency excursion to sub-phase duration for each pixel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the frequency excursion B is increased to expand the measurable distance range, then the measurement range is improved, but the noise increases and signal-to-noise ratio deteriorates
Solution Approach 1:
The patent divides the acquisition duration T into multiple sub-phases Ci, each with its own frequency excursion Bi. By segmenting the measurement process, the system can use smaller frequency excursions for each sub-phase, reducing noise while still achieving wide overall measurement range through multiple sequential measurements. The total distance range is obtained by combining results from multiple sub-phases with different Bi values.
2Productivity
If the acquisition rate is increased to capture more pixels simultaneously, then the productivity is improved, but the signal-to-noise ratio decreases due to reduced integration time
Solution Approach 1:
The patent employs periodic frequency modulation across multiple sub-phases, where each sub-phase represents a periodic cycle of measurement. By structuring the acquisition as periodic sub-phases with varying frequency excursions, the system maintains high acquisition rates while allowing sufficient integration time within each periodic cycle to preserve signal-to-noise ratio.
3Reliability
If the frequency excursion B is decreased to improve signal-to-noise ratio, then the signal-to-noise ratio is improved, but the measurable distance range is reduced
Solution Approach 1:
The patent systematically changes the frequency excursion parameter B across multiple sub-phases, using different Bi values for each sub-phase Ci. This parameter variation allows the system to optimize signal-to-noise ratio for each sub-phase while collectively covering a wide distance range. Each sub-phase uses parameters optimized for its specific measurement range, and the results are combined to achieve both high SNR and wide coverage.
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 enables accurate distance measurement across a wide range with improved signal-to-noise ratio, reducing errors and maintaining high acquisition rates, suitable for both snapshot and video applications.
Implementation Method 1
Pixel Pix comprises a photodetector PD, for example, a photodiode. Pixel Pix is configured so that its photodetector PD supplies a heterodyne signal iPD, for example, a photocurrent, having its amplitude depending on the intensity of the received beam 116.
Implementation Method 2
source 100 is controlled by sensor 1, for example, by a control circuit 118 of sensor 1, to modulate the optical frequency f of laser beam 102. More particularly, source 100 is controlled, or configured, so that the frequency f of beam 102 is modulated over a frequency range of width or excursion B for a time period T.
Implementation Method 3
Sensor 1 comprises an optical device 114 configured to superpose, or combine, reference beam 108 with the reflected beam 112. The superposition, by component 114, of the reflected beam 112 with reference beam 108 results in interferences in beam 116, which generate beats at a frequency FR depending on delay Δt
Implementation Method 4
Useful beam 106 is emitted towards a scene 110 to be imaged. In other words, beam 106 is used to illuminate scene 110. The reflection of beam 106 by scene 110 results in a reflected beam 112 which propagates from scene 110 to sensor 1.
Data Source
AI summary
The present description concerns a method of acquisition of distances from a sensor to a scene, comprising a number N of consecutive capture sub-phases Ci, with N an integer greater than or equal to 2 and i an integer index ranging from 1 to N, each sub-phase Ci comprising: supplying a laser beam having an optical frequency (f) linearly varying over a frequency range of width Bi for a time period Ti; delivering, from the laser beam, a reference beam and a useful beam; and illuminating the scene with the useful beam and illuminating at least one pixel row with a superposition of the reference beam and of a reflected beam. An absolute value of a ratio Bi/Ti is different for each capture sub-phase Ci.