TOF Sensor Dynamic Calibration via Sinusoidal Waveforms
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Solution Overview
Problem
Time-of-flight (TOF) systems face errors due to high-order harmonics in phase-based data, particularly when using square-wave optical energy waveforms, which affect calibration accuracy and require significant memory storage, making dynamic calibration challenging without increasing storage overhead.
Innovation Solution
Operating a TOF system with an odd number of phase shifts (e.g., 3, 5, 7) reduces bias error from high-order harmonics, allowing for dynamic calibration and enhanced modulation contrast while minimizing memory requirements, and optionally using look-up tables for finer corrections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If square-wave optical energy waveforms are used in phase-based TOF systems, then modulation contrast is enhanced, but high-order harmonics introduce bias error that degrades calibration accuracy
Solution Approach 1:
The patent changes the waveform parameter from square-wave to sinusoidal waveform. This parameter change eliminates high-order harmonics while maintaining adequate modulation contrast, thereby resolving the contradiction between enhanced modulation contrast and calibration accuracy. The sinusoidal waveform provides a clean single-frequency signal that avoids the harmonic distortion inherent in square-wave formulations.
2Measurement precision
If dynamic calibration is implemented to correct for system changes over time and temperature, then calibration accuracy is improved, but memory storage requirements increase significantly
Solution Approach 1:
The patent extracts and removes the need for complex dynamic calibration tables and lookup tables by using a sinusoidal waveform. The mathematical simplicity of sinusoidal-based phase measurement eliminates the requirement for storing extensive calibration data, thereby achieving calibration accuracy without increasing memory storage requirements.
Solution Approach 2:
The patent replaces expensive, memory-intensive dynamic calibration structures with a simple, fixed sinusoidal waveform approach. This substitution uses a computationally inexpensive and memory-efficient method that achieves comparable or superior calibration accuracy without requiring large storage resources.
3Reliability
If more calibration data is stored to account for system changes, then calibration robustness over time and temperature is improved, but device complexity and storage overhead increase
Solution Approach 1:
The patent changes the fundamental waveform parameter to sinusoidal, which inherently provides mathematical properties that are robust to system variations. This parameter change eliminates the need for complex calibration data structures, achieving reliability without increasing device complexity or storage overhead.
Data Source
Figure 1A~1C
Figure 1D~1E
Figure 2
AI summary
A phase-based TOF system preferably generates an optical waveform with fast rise and fall times, to enhance modulation contrast, notwithstanding there will be many high order harmonics. The system is preferably operated with an odd number of phases, to reduce system bias error due to the higher order harmonics, while maintaining good modulation contrast, without unduly increasing system memory requirements. Preferably the system can dynamically calibrate (and compensate for) higher order harmonics in the TOF generated optical energy waveform, over time and temperature. Within the optical energy transmission channel, or within the optical energy detection channel, detection amplifier gain may be modified, and/or detector signal integration time may be varied, and/or digital values may be employed to implement calibration and error reduction The resultant TOF system can operate with improved phase-vs-distance characteristics, with reduced calibration requirements.