ToF Pixel Structure with Transfer Gates for Ambient Light Suppression
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Solution Overview
Problem
Existing Time of Flight (ToF) distance measurement systems face challenges in accurately determining distance due to superposition of useful signals and ambient light, leading to reduced precision and increased laser energy requirements, especially in dynamic and fast-moving scenarios.
Innovation Solution
A pixel structure with a semiconductor substrate, a photoactive region, and multiple transfer gates configured to cyclically drive charge carriers to evaluating capacities, allowing for efficient ambient light suppression and distance measurement using a single laser pulse, thereby reducing laser energy consumption and increasing measurement speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional ToF systems use multiple laser pulses and continuous illumination to ensure accurate distance measurement, then measurement precision is improved, but laser energy consumption increases and measurement speed decreases
Solution Approach 1:
The patent applies periodic action by using a single laser pulse instead of continuous illumination or multiple pulses. The measurement process is synchronized with periodic transfer gate operations that cycle through different integration periods, allowing the system to capture signal and ambient light separately in different phases of the cycle, thereby achieving accurate distance measurement with minimal laser energy consumption.
Solution Approach 2:
The patent implements preliminary action by performing ambient light measurement during specific integration periods before the actual distance measurement. The transfer gates are pre-configured to direct ambient light charges to dedicated evaluation capacities during predetermined time windows, so that when the laser pulse arrives, the ambient light component has already been separately captured and can be subtracted from the total signal.
2Measurement precision
If conventional ToF systems use continuous illumination and multiple pulses to capture sufficient signal, then measurement precision is improved, but measurement speed decreases
Solution Approach 1:
The system uses periodic transfer gate operations that cycle through different integration periods within a single laser pulse cycle. This allows multiple measurements to be performed sequentially during different phases of the periodic cycle, enabling fast alternating measurements while maintaining precision through the periodic separation of signal and ambient light components.
Solution Approach 2:
The patent maintains continuity of useful action by continuously operating the transfer gates through all integration periods without interruption. The transfer gates switch between capturing signal charges and ambient light charges in a continuous cyclic manner, ensuring that the measurement process proceeds without idle time and achieving high measurement speed while preserving precision.
3Device complexity
If conventional ToF systems use single pixel structures without separate ambient light capture, then device complexity is reduced, but measurement precision deteriorates due to inability to suppress ambient light
Solution Approach 1:
The patent applies segmentation by dividing the pixel structure into functionally separate regions: a photoactive region for generating charges and multiple evaluation capacities for different charge types. Transfer gates segment the charge transport paths, directing signal charges and ambient light charges to different evaluation capacities. This segmentation enables precise ambient light suppression while maintaining a relatively simple overall pixel structure.
Solution Approach 2:
The transfer gates serve multiple functions: they transport signal charges during signal integration periods, transport ambient light charges during ambient light measurement periods, and can be reset to reference potentials. This multi-functionality allows the same hardware components to handle both signal capture and ambient light suppression without requiring entirely separate dedicated structures for each function.
4Device complexity
If conventional ToF systems use standard read-out methods without cyclic transfer gate operation, then device complexity is reduced, but ambient light suppression capability is lost
Solution Approach 1:
The read-out method uses periodic transfer gate operations that alternate between capturing signal charges and ambient light charges. The transfer gates are driven in a cyclic manner with different integration periods, creating a periodic measurement pattern that allows the system to distinguish and separate ambient light interference from the actual signal through temporal modulation and periodic sampling.
Solution Approach 2:
The system implements feedback by using the ambient light measurement captured during specific integration periods to compensate for and subtract ambient light interference from the signal measurement. The charges captured in the first evaluation capacities during ambient light periods are used as reference values to eliminate the harmful ambient light component from the final distance calculation.
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 enables precise distance measurement with reduced laser energy usage and improved speed, suitable for dynamic environments and fast-moving objects, by effectively separating and subtracting ambient light from the signal, and minimizing reset noise.
Implementation Method 1
a photoactive region integrated on the substrate for generating charge carriers responsive to radiation incident on the photoactive region
Data Source
AI summary
The present invention relates to a concept for optical distance measurement, wherein a radiation pulse is emitted in the direction of an object of measurement. At least two different transfer gates which couple a photoactive region to at least two different evaluating capacities are driven during different drive intervals so that charge carriers generated during the drive intervals by a radiation pulse reflected from the object of measurement and/or by ambient radiation can be transported from the photoactive region to the evaluating capacities each coupled to the at least two transfer gates. Another transfer gate is driven during a time outside the drive intervals of the at least two transfer gates to connect the photoactive region to a reference potential terminal acting as a charge carrier sink during the time outside the drive intervals of the at least two transfer gates.