ToF Histogram Peak Finding With Cross-Talk Rejection
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Solution Overview
Problem
Time-of-flight (ToF) imagers face challenges in efficiently processing histograms due to computational complexity and cross-talk, leading to false target detection and high computational requirements, which are typically addressed by off-chip processors, increasing costs and latency.
Innovation Solution
Implementing a zero-crossing filter (ZCF) and matched filter (MF) to process histograms, using weight coefficients to identify and classify peaks, and an adaptive target detection method to reject false targets caused by cross-talk, enabling on-chip processing and robust target detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If off-chip processors are used to process histograms, then measurement precision is improved, but device complexity and loss of time increase
Solution Approach 1:
The patent combines the histogram processing functions (filtering, peak finding, target detection) that were previously performed by separate off-chip processors into an integrated on-chip processing unit. This merging eliminates the need for external processors while maintaining detection accuracy, thereby reducing device complexity and inter-chip communication overhead.
Solution Approach 2:
The on-chip processing unit is designed to perform multiple functions including zero-crossing filtering, matched filtering, peak detection, and target classification within a single integrated circuit. This multi-functional approach replaces multiple specialized off-chip processors, reducing overall system complexity while preserving measurement precision.
2Measurement precision
If off-chip processors are used to process histograms, then measurement precision is improved, but loss of time increases
Solution Approach 1:
By integrating histogram processing functions into an on-chip unit, the patent eliminates data transfer time between chip and external processor. The combined filtering and peak finding operations are performed in-place, significantly reducing processing latency while maintaining detection accuracy.
Solution Approach 2:
The on-chip processing unit performs preliminary filtering and peak detection operations directly on the histogram data as it is generated, before further processing is needed. This preliminary action on-chip avoids the time penalty of transferring raw histogram data to off-chip processors for initial processing steps.
3Ease of operation
If cross-talk is not rejected, then ease of operation is maintained, but measurement precision deteriorates due to false target detection
Solution Approach 1:
The patent converts the harmful cross-talk signal into a detectable pattern by using zero-crossing filtering. The filter transforms cross-talk-induced distortions in the histogram into identifiable zero-crossing points, which then serve as markers for pulse region boundaries. This allows the system to automatically distinguish true targets from cross-talk artifacts, improving measurement precision while maintaining operational simplicity.
Solution Approach 2:
The zero-crossing filter acts as an intermediary between the raw histogram data and the peak detection algorithm. It processes the histogram to highlight zero-crossing points that indicate the presence or absence of cross-talk, enabling the subsequent peak finding circuit to accurately identify true targets without being misled by cross-talk interference.
4Productivity
If computational complexity is reduced, then productivity is improved, but measurement precision may deteriorate
Solution Approach 1:
The patent extracts only the essential features from the full histogram data by focusing on zero-crossing points and pulse region boundaries. Instead of performing computationally intensive analysis on the entire histogram, the system extracts key characteristics (zero-crossings) that are sufficient for accurate target detection, thereby improving processing efficiency while maintaining measurement precision.
Solution Approach 2:
The patent changes the parameter space by transforming the histogram data through zero-crossing filtering, which converts amplitude information into zero-crossing point locations. This parameter transformation simplifies the subsequent peak finding operation, reducing computational complexity while preserving the information needed for accurate target detection.
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
The solution reduces computational complexity, rejects false targets, and achieves robust and efficient on-chip processing, enhancing the detection range and reducing latency in ToF imagers.
Implementation Method 1
filtering the histogram using a zero-crossing filter (ZCF) to generate a ZCF output signal
Implementation Method 2
a matched filter (MF) configured to generate an MF output signal by filtering the histogram
Implementation Method 3
A reflected photon may generate a carrier in the SPAD through a photo electric effect
Implementation Method 4
The photon-generated carrier may trigger an avalanche current in one or more of the SPADs in an SPAD array
Data Source
AI summary
A method of processing a histogram generated by a time-of-flight (ToF) imager includes: filtering the histogram using a zero-crossing filter (ZCF) to generate a ZCF output signal; finding zero-crossing points in the ZCF output signal, where the zero-crossing points define one or more pulse regions in the ZCF output signal; computing, for each pulse region of the one or more pulse regions, a weighted sum of the pulse region; finding, in each pulse region, a maximum peak; classifying the maximum peak in each pulse region as a first type of peak or a second type of peak based on the weighted sum of the pulse region; and generating a list of ZCF targets from the maximum peaks classified as the first type of peaks.