Time-of-Flight Histogram Crosstalk Correction via Adaptive Filtering
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Solution Overview
Problem
Current time-of-flight ranging systems face challenges with pile-up and cross-talk issues, which affect distance measurement accuracy and require iterative SPAD selection and aperture placement, leading to reduced event counts and spatial subsampling, especially under high ambient light conditions.
Innovation Solution
The method involves processing histogram data from a photosensitive sensor to isolate and remove parasitic light path components, using adaptive width filters to filter out cross-talk and identify median values, and applying a pile-up correction algorithm to shape histogram data and correct for pile-up effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If iterative SPAD selection and aperture placement are used to correct cross-talk, then cross-talk correction is achieved, but device complexity and processing time increase
Solution Approach 1:
The patent captures cross-talk histograms during a calibration phase before actual distance measurements are taken. By pre-characterizing the cross-talk effects and storing them for later subtraction, the system avoids the need for iterative corrections during operation, thereby reducing device complexity and processing time while maintaining cross-talk correction capability.
2Object-affected harmful factors
If aperture placement is used to reduce cross-talk, then cross-talk is minimized, but spatial subsampling occurs reducing measurement coverage
Solution Approach 1:
The patent extracts and removes cross-talk components from the histogram data through mathematical subtraction of pre-captured cross-talk histograms. This approach eliminates the need for physical aperture placement, thereby minimizing cross-talk without imposing spatial subsampling constraints and preserving full sensor coverage.
3Measurement precision
If iterative correction methods are applied, then measurement accuracy improves, but processing time increases
Solution Approach 1:
The patent performs cross-talk characterization in advance during calibration and stores the results for direct subtraction during measurement. This preliminary action transforms a potentially iterative correction process into a single-step mathematical operation, maintaining high measurement accuracy while significantly reducing processing time during actual operation.
Solution Approach 2:
The system uses its own captured data (cross-talk histograms) to correct future measurements through simple subtraction. This self-service approach eliminates the need for complex iterative algorithms or external correction mechanisms, achieving accurate corrections efficiently.
4Adaptability or versatility
If high ambient light conditions are tolerated, then operational versatility is maintained, but pile-up effects increase reducing measurement accuracy
Solution Approach 1:
The patent extracts and removes pile-up components from the histogram data by identifying and subtracting the characteristic pile-up signal shape. This allows the system to maintain operational capability in high ambient light conditions while correcting the measurement accuracy that would otherwise be degraded by pile-up effects.
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 distance measurement accuracy by reducing the impact of pile-up and cross-talk, maintaining high event counts, and improving range resolution without spatial subsampling, even in challenging lighting conditions.
Implementation Method 1
A photon may generate a carrier in the SPAD through the photo electric effect. The photo generated carrier may trigger an avalanche current in one or more of the SPADs in an SPAD array.
Implementation Method 2
This method comprises sending a light signal towards the object and measuring the time taken by the signal to travel to the object and back. The calculation of the time taken by the signal for this travel may be obtained by measuring the phase shift between the signal coming out of the light source and the signal reflected from the object and detected by a light sensor.
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
A method for processing a histogram output from a detector sensor, the method comprising filtering histogram data to remove at least one parasitic light path component from the histogram data.