SPAD Array Gated Histogram Construction for TOF Depth Mapping
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Solution Overview
Problem
Current time-of-flight (TOF) imaging techniques face challenges in achieving fine distance resolution due to the limited time uncertainty of single-photon avalanche diodes (SPADs) at room temperature, which restricts the precision of depth mapping systems.
Innovation Solution
The implementation of adaptively gated detection methods, where each pixel undergoes a coarse measurement phase to estimate the time of flight (TOF) followed by a fine measurement phase within a narrow detection window, reducing memory requirements and background photon interference, using SPADs and processing circuits to identify and fix the optimal gating interval for each sensing element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If SPADs are used at room temperature for TOF measurement, then device complexity is reduced and ease of operation is improved, but measurement precision deteriorates due to limited time uncertainty resolution
Solution Approach 1:
The measurement process is divided into multiple acquisition periods, each with a specific gating interval. Instead of attempting to measure all photons simultaneously with high precision, the system segments the temporal measurement space into discrete windows that are sequentially activated. This allows the use of simpler room-temperature SPADs while achieving fine effective resolution through multiple coarse measurements.
Solution Approach 2:
The system performs preliminary coarse measurements during a first sequence of acquisition periods to identify detection windows before performing fine measurements. The gating intervals are swept through different time positions in advance to locate regions containing photon arrivals, which then guides subsequent high-precision measurements. This preliminary action enables the system to achieve fine resolution without requiring the SPADs themselves to have inherently fine time uncertainty.
2Measurement precision
If histograms are built over many measurement cycles to achieve fine distance resolution, then measurement precision is improved, but loss of time increases due to the number of cycles required
Solution Approach 1:
The system performs a preliminary sweeping phase where gating intervals are moved through different time positions to quickly identify detection windows containing photon arrivals. This preliminary action prevents wasting measurement cycles on time positions where no photons are present, significantly reducing the total number of cycles needed to build accurate histograms and thereby reducing measurement time.
Solution Approach 2:
The system extracts and isolates only the relevant time regions (detection windows) where photon arrivals occur, based on information from the first sequence of acquisition periods. By taking out and focusing measurements only on these identified windows during the second sequence, the system avoids unnecessary measurements in other time regions, improving both precision and speed.
3Adaptability or versatility
If the gating interval is fixed for all sensing elements, then device complexity is reduced, but adaptability deteriorates as different detection windows are needed for different sensing elements
Solution Approach 1:
The gating intervals are made dynamic rather than fixed, allowing them to be independently adjusted for each sensing element based on its specific detection window. The gating generator dynamically sets the start time of gating intervals for different sensing elements according to their individual requirements, enabling each element to operate optimally for its specific measurement range while maintaining a unified control architecture.
4Reliability
If memory records all photon arrival times without gating to maintain simplicity, then ease of operation is improved, but loss of substance increases due to background photon interference
Solution Approach 1:
The system extracts and records only photons that arrive during the specific gating intervals, excluding all other photons. By taking out the relevant time window and recording photons only within this window, the system effectively filters out background photons and noise that occur outside the gating interval, significantly improving signal quality and reducing false detections without requiring complex post-processing filtering.
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 temporal resolution of TOF measurements, allowing for more precise depth mapping with reduced memory needs and improved rejection of background photons, thereby improving the accuracy of depth maps.
Implementation Method 1
Single-photon avalanche diodes (SPADs), also known as Geiger-mode avalanche photodiodes (GAPDs), are detectors capable of capturing individual photons with very high time-of-arrival resolution
Implementation Method 2
A gating generator, which is configured to variably set a start time of the gating interval for each sensing element within each acquisition period
Data Source
AI summary
A sensing device includes a first array of sensing elements, which output a signal indicative of a time of incidence of a single photon on the sensing element. A second array of processing circuits are coupled respectively to the sensing elements and comprise a gating generator, which variably sets a start time of the gating interval for each sensing element within each acquisition period, and a memory, which records the time of incidence of the single photon on each sensing element in each acquisition period. A controller sets, in each of at least some of the acquisition periods, different, respective gating intervals for different ones of the sensing elements.