SPAD Array Sensitivity Segmentation for Near-Range LiDAR
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Solution Overview
Problem
Existing light signal reception systems, particularly in LiDAR systems, face challenges due to the 'dead time' of single-photon avalanche diodes (SPADs), which limits detection in the near range and can be incapacitated by low back-scattering from front panels, preventing the detection of objects close to the sensor.
Innovation Solution
The use of two groups of light-receiving elements with different sensitivities, where one group is deactivated during laser emission to manage the dead time, allowing for near-range detection by activating lower sensitivity SPADs during emission and higher sensitivity SPADs during other times, with the help of an evaluation circuit and a mask to control sensitivity and spatial alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-sensitivity SPADs are used for far-range detection, then detection sensitivity is improved, but dead time increases causing near-range detection failure
Solution Approach 1:
The receiving elements are divided into multiple groups with different sensitivity levels. High-sensitivity SPADs are segmented from low-sensitivity SPADs, allowing each group to handle different detection scenarios. This segmentation resolves the contradiction by enabling high-sensitivity detection for far-range objects while using low-sensitivity detection for near-range objects during the dead time period.
Solution Approach 2:
Different receiving elements are assigned different sensitivity characteristics based on their spatial and functional requirements. The system applies local quality by having specific elements (high-sensitivity SPADs) optimized for far-range detection while other elements (low-sensitivity SPADs) are optimized for near-range detection, allowing simultaneous optimization for both ranges without compromise.
2Length of moving object
If light emission power is increased for far-range detection, then detection range is improved, but back-reflection incapacitates the receiver
Solution Approach 1:
The system employs periodic switching between high-sensitivity and low-sensitivity receiving modes synchronized with the light emission cycle. During light emission periods, low-sensitivity modes are activated to withstand back-reflection; during non-emission periods, high-sensitivity modes are activated for far-range detection. This periodic action resolves the contradiction by temporal separation of the conflicting requirements.
Solution Approach 2:
Low-sensitivity SPADs act as intermediaries that can handle the high light power and back-reflection conditions during emission, protecting the high-sensitivity SPADs from incapacitation. The intermediary elements absorb the harmful back-reflection impact while the primary high-sensitivity elements remain protected for their specialized detection function.
3Device complexity
If single group of SPADs is used, then device complexity is reduced, but near-range and far-range detection cannot be simultaneously achieved
Solution Approach 1:
The receiving element array is designed with multi-functionality, where different groups of SPADs can be selectively activated based on detection requirements. The same physical array serves both near-range and far-range detection functions by dynamically reconfiguring which element groups are active, achieving universality without requiring separate dedicated detector arrays for each range.
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
Enables reliable detection of objects up to 3 meters in the near range by effectively managing dead time and sensitivity, preventing direct optical crosstalk and maintaining system functionality despite low back-scattering, while maintaining performance for far-range detection.
Implementation Method 1
single-photon detectors SPDs are used to receive. It is further indicated that this type of detector, to which SPADs (single-photon avalanche diodes) belong
Implementation Method 2
with the help of an evaluation circuit and a mask to control sensitivity and spatial alignment
Implementation Method 3
A system and a method for measuring the phase of a modulated optical signal is known from U.S. 2004/0233942 A1
Data Source
AI summary
A receiving arrangement for receiving light signals and a method for receiving light signals are proposed, wherein a light receiver is provided, which serves for receiving the light signals and converting them into electrical signals. Furthermore, an evaluation circuit is provided, which, depending on the electrical signals and a start signal for the emission of the light signals, determines a distance between the receiving arrangement and an object at which the light signals are reflected. A characterizing feature is that the light receiver has a first group of light-receiving elements, which has a higher sensitivity for receiving the light signals than at least one further group of light-receiving elements, wherein the first and the further groups are ready for reception at different times.