ToF Histogram Rising Edge Fitting for Distance Accuracy
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Solution Overview
Problem
Time-of-flight ranging systems face challenges in accurately estimating target distances due to pulse shape distortion and computational complexity, especially when dealing with multiple targets or close-range measurements, which limits their integration and efficiency.
Innovation Solution
A method that involves identifying the rising edge of a histogram corresponding to a reflected light pulse, fine-tuning its location through a fitting process with a pre-stored high-resolution rising edge, and calculating the target distance by adding a pre-determined offset, allowing for robust distance estimation immune to pulse shape distortions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional histogram processing methods are used to estimate target distance, then the system can operate with simpler processing architecture, but the measurement precision deteriorates due to pulse shape distortion and merging of multiple targets
Solution Approach 1:
The patent segments the histogram processing into distinct functional stages: coarse rising edge detection using simple thresholding, fine-tuning through fitting with pre-stored high-resolution rising edges, and distance calculation. This segmentation allows the system to achieve high measurement precision through the fitting process while maintaining relatively simple processing architecture through the efficient coarse detection stage.
Solution Approach 2:
The patent employs preliminary action by pre-storing high-resolution rising edges during system initialization or calibration. These pre-stored rising edges are then used during actual measurement to fine-tune the detected rising edge locations through fitting, significantly improving measurement precision without requiring complex real-time processing.
2Productivity
If off-chip processor is used for histogram processing, then the computational tasks can be performed with sufficient processing power, but the device complexity and integration level worsen due to separate semiconductor dies
Solution Approach 1:
The patent merges the histogram processing functions directly into the SPAD array chip by integrating the rising edge detection circuitry and fitting processing units within the same semiconductor die. This consolidation eliminates the need for separate off-chip processors, reducing device complexity and integration barriers while maintaining processing efficiency through the optimized on-chip architecture.
Solution Approach 2:
The patent implements self-service by enabling the SPAD array system to perform its own histogram processing and distance estimation internally, without requiring external processing resources. The integrated circuit performs all necessary computations including coarse detection, fine-tuning via fitting, and distance calculation, making the system self-sufficient and reducing overall system complexity.
3Device complexity
If simple rising edge detection is used, then the processing complexity is reduced, but the measurement precision deteriorates due to inability to handle pulse shape distortion
Solution Approach 1:
The patent applies parameter changes by transforming the simple binary rising edge detection into a multi-parameter fitting process. The system adjusts the rising edge location parameter through comparison with pre-stored high-resolution rising edges, allowing it to compensate for pulse shape distortions while maintaining relatively simple processing complexity through the use of pre-computed reference data.
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 accurate estimation of target distances with immunity to pulse shape distortions and reduces computational complexity, facilitating higher integration and efficiency in time-of-flight ranging systems.
Implementation Method 1
A reflected photon may generate a carrier in the SPAD through the photo electric effect. The photon-generated carrier may trigger an avalanche current in one or more of the SPADs in an SPAD array.
Implementation Method 2
A ToF ranging system uses a ToF imager to measure the distance of an object (e.g., a target). To measure an object, the ToF ranging system instructs the ToF sensor to send a light signal (e.g., light pulses) towards the object and measures the time taken by the signal to travel to the object and back.
Implementation Method 3
the ToF ranging system instructs the ToF sensor to send a light signal (e.g., light pulses) towards the object
Data Source
AI summary
A method of ranging using a time-of-flight (ToF) ranging system includes: receiving, by a processor, a histogram generated by a ToF imager of the ToF ranging system, where the ToF imager is configured to transmit a light pulse for ranging purpose; finding a rising edge of a pulse region in the histogram, where the pulse region corresponds to a reflected light pulse from a target; fine-tuning a location of the rising edge by performing a fitting process between the rising edge and a pre-stored high-solution rising edge; and calculating an estimate of a distance of the target by adding a pre-determined offset to a distance of the rising edge after fine-tuning the location of the rising edge.