Time-of-Flight Depth Mapping Using Multiple Pulse Repetition Intervals
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Solution Overview
Problem
Existing time-of-flight (ToF) depth mapping systems face challenges with low signal/noise ratio (SNR) and range folding, particularly when incorporated into mobile devices where radio frequency interference can degrade performance.
Innovation Solution
The system employs multiple pulse repetition intervals (PRIs) to improve SNR and resolve range folding. Processing and control circuitry selects and drives different PRIs to emit sequences of pulses, allowing for the computation of depth coordinates by analyzing the times of flight of the pulses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single pulse repetition interval (PRI) is used in ToF depth mapping, then the measurement process is simple and fast, but range folding occurs at distances beyond the range limit defined by the PRI
Solution Approach 1:
The system dynamically switches between multiple PRIs (first PRI, second PRI greater than first, third PRI greater than second) based on the depth coordinates being measured. This allows the measurement range to be adapted to different scene depths, resolving range folding while maintaining measurement efficiency through selective PRI usage.
Solution Approach 2:
The invention changes the PRI parameter across different measurement sequences. By using a first sequence at first PRI, second sequence at second PRI, and third sequence at third PRI, the system expands the measurable depth range and resolves range folding ambiguities that would occur with a single fixed PRI.
2Measurement precision
If multiple pulse repetition intervals (PRIs) are used to resolve range folding, then depth accuracy is improved, but the device complexity increases
Solution Approach 1:
The system employs periodic pulse sequences at different PRIs (first sequence, second sequence, third sequence) to measure depth. By systematically alternating between multiple PRIs and processing the combined results, the system achieves high depth accuracy while managing complexity through structured periodic measurement cycles.
3Measurement precision
If a short pulse repetition interval (PRI) is used, then the range limit is reduced and range folding is avoided, but the maximum measurable depth is limited
Solution Approach 1:
The system dynamically selects from multiple PRIs (first PRI for shorter ranges, second and third PRIs for extended ranges) based on the actual depth coordinates in the scene. This dynamic adaptation allows the system to maintain high range resolution for nearby objects while extending the maximum measurable depth for distant objects.
Solution Approach 2:
By changing the PRI parameter across different measurement sequences (first sequence at first PRI, second sequence at second PRI, third sequence at third PRI), the system achieves both high range resolution and extended maximum depth range, resolving the contradiction between range limit and measurable depth.
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 signal/noise ratio and effectively resolves range folding issues, enabling accurate depth mapping over a wider range while minimizing interference with radio transceivers in mobile devices.
Implementation Method 1
measuring the round-trip time, i.e. time-of-flight (ToF), taken by the optical beams as they travel from the source to the target scene and back to a detector array
Implementation Method 2
Some ToF systems use single-photon avalanche diodes (SPADs), also known as Geiger-mode avalanche photodiodes (GAPDs), in measuring photon arrival time
Data Source
AI summary
Sensing apparatus includes a radiation source, which emits pulses of optical radiation toward multiple points in a target scene. A receiver receives the optical radiation that is reflected from the target scene and outputs signals that are indicative of respective times of flight of the pulses to and from the points in the target scene. Processing and control circuitry selects a first pulse repetition interval (PRI), a second PRI, greater than the first PRI, and a third PRI, greater than the second PRI, from a permitted range of PRIs, drives the radiation source to emit sequences of the pulses at the first PRI, the second PRI, and the third PRI, and processes the signals output by the receiver in response to the first, second, and third sequences of the pulses in order to compute respective depth coordinates of the points in the target scene.