Non-Avalanche Depth Sensor With Multi-Photowell Fast Readout
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Solution Overview
Problem
Conventional 3D imagers and depth sensors face challenges with high dark current, low quantum efficiency, low spatial resolution, and impractically long read-out latency due to the use of avalanche-gain photodetectors, which hinder accurate depth measurement and sensitivity.
Innovation Solution
The development of low-latency, multi-photowell light sensors with pinned photodiodes and JFET-based devices that reduce read-out latency to sub-nanosecond levels, combined with advanced analog front ends and time-to-digital converters for rapid signal digitization, enabling higher sensitivity and resolution in depth sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If avalanche-gain photodetectors (SPADs, SiPMs) are used, then sensitivity to single photons is improved, but dark current increases and noise increases
Solution Approach 1:
The photodetector is segmented into multiple independent photowells (e.g., first photowell, second photowell, third photowell) instead of using a single large photowell. Each photowell independently collects photons and generates charge carriers. This segmentation reduces dark current accumulation and allows parallel readout, improving sensitivity while controlling noise levels.
Solution Approach 2:
The patent replaces the avalanche multiplication mechanism (mechanical/electrical gain process) with a direct charge collection and transfer mechanism. Instead of relying on avalanche gain which amplifies both signal and noise, the system uses multiple photowells with direct charge transfer to floating diffusion nodes, achieving sensitivity through parallel architecture rather than signal amplification.
2Reliability
If pinned photodiode read-out by photocharge transfer to floating diffusion node is used, then robustness and quantum efficiency are improved, but read-out latency increases to hundreds of nanoseconds
Solution Approach 1:
The single photodetector pixel is segmented into multiple photowells (first, second, third photowells) that can be read out in parallel. Each photowell has its own floating diffusion node, allowing simultaneous charge transfer and readout operations. This parallel architecture reduces the effective read-out latency by dividing the total readout time across multiple channels.
Solution Approach 2:
The patent implements preliminary charge transfer from photowells to floating diffusion nodes during the integration period, preparing the signal for rapid readout. The pinned photodiode structure pre-positiones charge carriers in the depletion region, enabling faster transfer compared to standard photodiodes, thereby reducing the overall read-out latency while maintaining robustness.
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 solution dramatically improves depth sensing accuracy and sensitivity by reducing read-out latency by several orders of magnitude, allowing for precise distance measurements and enhanced photon-counting capabilities, surpassing the limitations of conventional avalanche-gain sensors.
Implementation Method 1
a light sensor in a pulse-based system intended measure a distance/depth with 5 mm accuracy will need to resolve the round-trip flight time of the light pulse
Implementation Method 2
the charge-transfer time alone is typically on the order of hundreds of nanoseconds (equivalent to a distance measurement resolution of hundreds of meters)
Data Source
AI summary
A sensing device includes a light source to emit light, a light sensor to detect reflection of the emitted light and distance determination circuitry responsive to reflected-light detection within the light sensor. The light sensor includes a photodetector having a photocharge storage capacity in excess of one electron and an output circuit that generates an output signal responsive to light detection within the photodetector with sub-hundred nanosecond latency. The distance determination circuitry measures an elapsed time based on transition of the output signal in response to photonic detection within the photodetector and determines, based on the elapsed time, a distance between the sensing device and a surface that yielded the reflection of the emitted light.