Time-of-Flight Apparatus Using Segmented Light Pulses for SNR
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Solution Overview
Problem
Time-of-flight (ToF) systems face challenges in obtaining high signal-to-noise ratio (SNR) values at long distances or under strong ambient light conditions, due to limitations in active illumination intensity imposed by eye safety regulations.
Innovation Solution
A ToF apparatus and method that divide a frame into active light time intervals during which light is emitted to the scene, reducing exposure time while maintaining the same total light energy, thus improving SNR without violating eye safety standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the active illumination intensity is increased to improve SNR, then the signal-to-noise ratio improves, but eye safety regulations are violated
Solution Approach 1:
The light source emits light in periodic pulses rather than continuously. Each frame is divided into multiple active light time intervals where light is emitted, separated by dark intervals. This periodic emission pattern allows the peak intensity during active intervals to be high enough for good SNR, while the average intensity over the full frame remains within eye safety limits.
Solution Approach 2:
The illumination pattern is made dynamic by varying the light emission within each frame. The system transitions from static continuous illumination to dynamic pulsed illumination, where the light source is actively turned on and off during the frame acquisition period. This dynamic control enables temporal separation of high-intensity signaling from low-intensity averaging.
2Measurement precision
If the light emission duration is extended to accumulate more light energy, then the SNR improves, but the exposure time increases causing motion blur
Solution Approach 1:
Instead of using a single long continuous exposure, the system employs multiple short periodic light pulses within the frame. Each active light time interval is brief, freezing motion effectively, while multiple such intervals accumulate sufficient light energy through temporal summation in the depth calculation algorithm.
Solution Approach 2:
The frame acquisition time is segmented into multiple discrete active light time intervals separated by dark intervals. Rather than one continuous exposure, the total light accumulation is achieved through multiple segmented pulses, each contributing to the overall signal while maintaining short individual exposure durations that prevent motion blur.
3Measurement precision
If the light energy is concentrated in a short time interval, then the peak intensity increases improving SNR, but the total light energy decreases
Solution Approach 1:
The system uses periodic light pulses where each pulse has high peak intensity for good SNR. The total light energy is maintained by emitting multiple such pulses within a frame, with the cumulative energy from all active light time intervals providing sufficient illumination while keeping each individual pulse brief and intense.
Solution Approach 2:
Although individual pulses are short, the useful action of light emission continues throughout the frame through multiple repeated pulses. The light source repeatedly emits energy in active light time intervals, ensuring continuous accumulation of total light energy while maintaining high peak intensities during each emission event.
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
The solution effectively enhances the SNR in ToF systems by distributing the light energy over shorter active intervals, reducing noise from ambient light, and ensuring compliance with eye safety regulations.
Implementation Method 1
a light source for emitting light to a scene; a light detector for detecting light from the scene
Data Source
AI summary
A time-of-flight apparatus has: a light source for emitting light to a scene; a light detector for detecting light from the scene; and a control, the control being configured to: acquire a frame of detected light from the light detector, wherein the frame corresponds to a predetermined time interval, and drive the light source for emitting light during the acquisition of the frame, wherein the light energy accumulated within the frame has a predetermined value, and wherein the frame is divided into active light time intervals during which light is emitted to the scene.