CW Time-of-Flight Modulation Using Harmonic-Canceling Waveforms
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Solution Overview
Problem
Continuous Wave (CW) ToF camera systems face challenges in generating sinusoidal signals, which are costly and difficult to produce, while non-sinusoidal signals like square waves are easier but suffer from significant harmonic content that reduces measurement accuracy.
Innovation Solution
Utilizing two or more non-sinusoidal control signals, such as square or trapezoidal waves, with different duty cycle ratios to combine into a single modulated signal that approximates a sinusoidal signal, thereby reducing harmonic energy and maintaining system accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sinusoidal control signals are used to modulate the light source, then measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent combines multiple non-sinusoidal control signals (first and second modulated control signals) to produce a combined signal that approximates a sinusoidal waveform. This merging approach achieves the measurement accuracy of sinusoidal signals while using simpler non-sinusoidal signal generation methods, thereby reducing device complexity and cost.
Solution Approach 2:
The patent creates a composite control signal by combining multiple non-sinusoidal signals with different duty cycle ratios. This composite signal exhibits sinusoidal characteristics in its harmonic content, providing accurate measurements while avoiding the complexity of generating pure sinusoidal signals through traditional oscillators or waveform generators.
2Device complexity
If non-sinusoidal control signals are used to modulate the light source, then device complexity is reduced, but harmonic content increases reducing measurement accuracy
Solution Approach 1:
The patent converts the harmful harmonic content of non-sinusoidal signals into a beneficial outcome by combining multiple non-sinusoidal signals with different duty cycle ratios. The combination causes harmonic cancellation effects, where the harmonic content of individual signals interferes destructively, reducing overall harmonic distortion and improving measurement accuracy while maintaining simple signal generation.
3Object-generated harmful factors
If multiple non-sinusoidal control signals are combined, then harmonic content is reduced, but control signal complexity increases
Solution Approach 1:
The patent changes key parameters of the control signals, specifically the duty cycle ratios of the first and second modulated control signals. By optimizing these duty cycle parameters, the combined signal achieves reduced harmonic content while maintaining a manageable control architecture. The parameter optimization balances harmonic reduction with control simplicity.
Data Source
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AI summary
The disclosure provides different time of flight, ToF, methods and systems for using two or more non-sinusoidal control signals to achieve modulated output light and/or image sensor control with reduced harmonic content. In particular, the two or more non-sinusoidal control signals have different relative phase offsets or duty cycle ratios such that a combined signal resulting from combing the two or more control signals has reduced harmonic content. By utilising non-sinusoidal signals and effectively making using of the combined signal for the output light and/or image sensor control, the system is more straightforward and lower cost to implement compared with systems that use sinusoidal control signals, whilst still maintaining accuracy of the system by minimising the harmonic noise normally associated with non-sinusoidal signals.