Multistage Demodulation Pixel for 3D Time-of-Flight Imaging
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Solution Overview
Problem
Current pixel architectures for demodulating modulated light signals face challenges in accurately transferring photo-generated charges due to slow transport speed, leading to inaccurate depth information, especially when sampling and storing only two phases, which requires multiple exposures and results in motion artifacts from fast-moving objects.
Innovation Solution
A demodulation pixel design with a photosensitive area and multiple stages of switches and storage sites, utilizing lateral drift fields to enable fast charge transfer and sampling of multiple phases within a single exposure, allowing for the storage of multiple samples and simultaneous modulation frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If photo-charges are transferred through the photo-sensitive detection region to storage area using step-wise potential distribution, then charges can be transported through the semiconductor substrate, but the transport speed is slow due to thermal diffusion dominating instead of fast lateral electric drift fields
Solution Approach 1:
The patent applies dynamic control of potential distribution through time-varying control signals applied to control electrodes. The potential distribution is dynamically adjusted during different time intervals to first accelerate charges laterally using strong electric drift fields, then guide them vertically to storage nodes, resolving the contradiction between transport speed and demodulation accuracy.
2Productivity
If only two integration nodes are used to accumulate photo-generated charges during certain time intervals, then demodulation can be performed, but multiple exposures are required which results in motion artifacts from fast-moving objects
Solution Approach 1:
The patent extends the storage dimension by providing multiple storage nodes (first storage node and second storage node) for each demodulation phase. This allows simultaneous storage of multiple phase samples within a single exposure, enabling higher sampling rates and eliminating motion artifacts without requiring multiple sequential exposures.
3Device complexity
If a single switch is used to transfer photo-generated electrons to storage sites, then device complexity is reduced, but multiple exposures are required to capture enough samples for depth reconstruction
Solution Approach 1:
The patent segments the charge transfer function by providing separate transfer paths with different control mechanisms. First control electrodes generate lateral electric fields for fast charge acceleration to intermediate regions, while second control electrodes control vertical charge transfer to specific storage nodes. This segmentation enables multi-phase sampling within single exposure without requiring complex multi-switch configurations at each pixel.
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 design enables accurate and efficient sampling and storage of multiple phases during a single exposure, reducing motion artifacts and improving depth information accuracy, while also allowing for increased ambiguity range and resolution in 3D imaging systems.
Implementation Method 1
the photosensitive area includes a lateral drift field for transferring the photo-charges in the photosensitive area toward the first stage switch
Implementation Method 2
a photosensitive area in which photo-charges are generated
Data Source
AI summary
A demodulation structure for a n-tap pixel, mainly for 3D time-of-flight (TOF) applications uses a 2-stage switch structure for demodulating a modulated electromagnetic wave. An almost arbitrary number of storage sites per pixel can be implemented enabling an almost arbitrary number of samplings captured during one exposure. It also provides the option to demodulate and integrate different phasing samples according to the different modulation frequencies within the same exposure.