Imaging Array Pixel Background Light Subtraction for LIDAR
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Solution Overview
Problem
Current LIDAR systems face limitations in range and accuracy due to the low optical power of semiconductor lasers and the impracticality of mechanically rotating elements, which restricts their use in automotive applications and miniaturization.
Innovation Solution
A method for background light subtraction in imaging arrays using a pixel with two charge storage wells allows for the integration and subtraction of background illumination, enabling the use of low-power VCSELs with extended pulse durations to increase the total light energy and range, while also employing range gating and high dynamic range detectors to enhance detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If semiconductor lasers with low optical power are used, then the system is compact and suitable for automotive applications, but the detection range is limited
Solution Approach 1:
The patent uses periodic pulsed illumination instead of continuous wave illumination. By concentrating the low-power laser energy into short nanosecond pulses, the system achieves high peak power during the pulse duration while maintaining low average power. This allows the low-power semiconductor laser to illuminate targets at extended ranges sufficient for automotive applications (up to 150m), resolving the contradiction between compact system size and detection range.
Solution Approach 2:
The patent performs preliminary background light measurement during a dedicated background measurement period before the actual ranging measurement. This background light information is then subtracted from the signal to improve detection accuracy. By preparing and storing background information in advance, the system can accurately detect weak reflected signals from distant targets using low-power lasers without being overwhelmed by ambient light.
2Adaptability or versatility
If mechanically rotating scanning elements are used, then 3D mapping capability is achieved, but the system complexity and size increase
Solution Approach 1:
The patent replaces mechanical rotating scanning systems with a stationary imaging array detector. The system uses a fixed semiconductor laser that illuminates the entire scene simultaneously, and the imaging array captures reflected light from all directions at once. This eliminates mechanical moving parts while maintaining 3D mapping capability through time-of-flight measurements for each pixel, resolving the contradiction between versatility and device complexity.
Solution Approach 2:
The patent transitions from 1D point-by-point scanning to 2D parallel imaging using an imaging array detector. Each pixel in the array independently measures the time-of-flight for its corresponding scene location, enabling simultaneous acquisition of depth information across the entire field of view. This dimensional transition from sequential to parallel measurement achieves 3D mapping without mechanical scanning components.
3Use of energy by moving object
If pulse duration is extended to increase total light energy, then detection range improves, but background light interference increases
Solution Approach 1:
The patent extracts and removes background light interference from the measured signal through background subtraction. The system performs a background measurement during a period when no laser pulse is emitted, capturing only ambient light. This background information is then subtracted from the signal obtained during laser illumination, isolating the reflected laser signal from background interference. This allows extended pulse durations to increase total energy while maintaining signal quality.
Solution Approach 2:
The patent applies preliminary anti-action by measuring and storing background light levels before the actual ranging measurement, then using this information to counteract background interference. By preparing the background subtraction reference in advance, the system can accurately recover weak reflected signals even when using extended pulse durations that would otherwise be overwhelmed by ambient light.
4Length of stationary object
If high optical power is used to extend detection range, then range increases, but the system requires high power components that are not suitable for automotive applications
Solution Approach 1:
The patent employs periodic pulsed operation to achieve high peak optical power from low-average-power semiconductor lasers. By concentrating energy into short nanosecond pulses with high peak power, the system extends detection range to automotive-relevant distances (up to 150m) while maintaining low average power consumption suitable for vehicle power budgets and thermal management constraints.
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 a compact, semiconductor-based time-of-flight system to achieve the required power and performance for automotive applications, extending the detection range and improving accuracy without increasing the optical power requirements.
Implementation Method 1
a first quantity of incident light received in the first pixel during a predetermined time
Implementation Method 2
decreasing the accumulated charge in proportion to a second quantity of incident light received in the first pixel during the predetermined time
Implementation Method 3
time-of-flight based sensing systems to be used for the characterization of a scene
Data Source
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AI summary
The invention pertains to a method for subtracting background light from an exposure value of a first pixel in an imaging array, said first pixel receiving a reflection of a spot from a scenery illuminated by a periodically pulsed pattern of spots, said periodically pulsed pattern comprising in alternation an illuminated phase and a non-illuminated phase, the method comprising: accumulating in said first pixel a charge in proportion to a first quantity of incident light, received in said first pixel while detecting said spot during a predetermined amount of time; and decreasing said charge in proportion to a second quantity of incident light received during said predetermined amount of time in absence of said spot. The invention also pertains to a pixel and an imaging array.