ToF Pulse Repetition Interval Selection for Range Folding
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Solution Overview
Problem
Time-of-flight (ToF) depth sensing systems face challenges with low signal/noise ratio (SNR) due to range folding and interference from harmonics generated by high pulse repetition frequency (PRF), particularly in mobile communication devices where radio transceivers are affected by these harmonics, limiting the range and accuracy of depth mapping.
Innovation Solution
The system employs multiple pulse repetition intervals (PRIs) to resolve range folding and minimize harmonic interference by selecting PRIs that avoid the frequency band of radio transceivers, allowing for enhanced depth coordinate computation and reduced noise, thereby improving the SNR and range of depth mapping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high pulse repetition frequency (PRF) is used in ToF depth sensing, then the depth mapping speed and resolution are improved, but harmonic interference with radio transceivers increases and range folding occurs
Solution Approach 1:
The system dynamically adjusts the pulse repetition interval (PRI) based on the operating conditions and radio frequency band usage. By making the PRI variable rather than fixed, the system can adapt to different scenarios - using shorter PRIs for high-speed mapping when radio interference is minimal, and longer PRIs when harmonic interference becomes problematic, thus resolving the contradiction between mapping speed and interference reduction
Solution Approach 2:
The system changes the temporal parameter (pulse repetition interval) to avoid harmonic frequencies that interfere with radio transceivers. By adjusting the PRI, the fundamental frequency and its harmonics shift away from radio bands, reducing interference while maintaining adequate mapping performance. This parameter adjustment directly addresses the contradiction by modifying the operating characteristics of the depth sensing system
2Measurement precision
If high pulse repetition frequency (PRF) is used, then the depth coordinate resolution is improved, but range folding occurs limiting the measurable distance
Solution Approach 1:
The system uses multiple pulse repetition intervals in a periodic sequence, alternating between different PRIs. This periodic variation allows the system to maintain high resolution during periods with shorter PRIs while using longer PRIs during other periods to extend the unambiguous range and prevent range folding. The periodic switching between different intervals resolves the contradiction between resolution and range accuracy
Solution Approach 2:
The system dynamically selects and switches between multiple pulse repetition intervals based on the measured distance to targets. When targets are within the unambiguous range of a short PRI, the system uses that shorter interval for higher resolution. When targets approach the range limit, the system switches to a longer PRI to prevent range folding, thus maintaining reliability while preserving measurement precision
3Measurement precision
If multiple pulse repetition intervals are used to reduce harmonic interference, then the SNR is improved, but the system complexity increases
Solution Approach 1:
The system segments the depth mapping process into multiple phases, each using a different pulse repetition interval. By dividing the overall measurement into sequential segments with different PRIs, the system can process data from each segment separately and combine results to achieve high SNR. This segmentation approach manages complexity by breaking down the problem into manageable, sequential tasks rather than requiring simultaneous complex operations
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 effectively disambiguates range folding and reduces harmonic interference, enabling accurate and extended-range depth mapping while maintaining high resolution and minimizing interference with radio communications.
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 (GAPD), in measuring photon arrival time
Data Source
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AI summary
Sensing apparatus (20) includes a radiation source (21), which emits pulses of optical radiation toward multiple points in a target scene (32). A receiver (23) 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 (26, 28, 35) selects a first pulse repetition interval (PRI) and a second PRI, greater than the first PRI, from a permitted range of PRIs, drives the radiation source to emit a first sequence of the pulses at the first PRI and a second sequence of the pulses at a second PRI, and processes the signals output in response to both the first and second sequences of the pulses in order to compute respective depth coordinates of the points in the target scene.