Non-Avalanche Depth Sensor Readout for Low-Latency Photon Detection
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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 and sensitive depth measurement.
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, enabling rapid and resolute signal digitization through improved analog front ends and time-to-digital converters.
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 patent extracts the avalanche gain function from the photodetector itself and implements it separately in post-detection electronics. The photodetector operates in linear mode without internal gain, eliminating avalanche-related dark current and noise, while electronic amplification provides the necessary signal enhancement after detection.
Solution Approach 2:
The patent replaces the physical/chemical avalanche multiplication process in semiconductor materials with an electronic amplification system. This substitution eliminates the inherent noise and dark current problems of avalanche photodetectors while maintaining signal amplification capability through electronic means.
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 patent implements preliminary charge accumulation in the photodetector's potential well before readout. By pre-collecting photocharges during the integration period and then rapidly transferring them to the readout node, the system achieves both high quantum efficiency (through extended collection) and low latency (through fast readout triggering).
Solution Approach 2:
The patent introduces dynamic control of the readout process through a trigger mechanism. The floating diffusion node remains in a high-impedance state during integration and only rapidly accepts charge when triggered by sufficient signal accumulation, enabling adaptive readout timing that minimizes latency while maintaining robustness.
3Manufacturing precision
If conventional four-transistor imaging pixel with pinned photodiode is used, then manufacturing yield and spatial resolution are improved, but charge-transfer time increases to hundreds of nanoseconds
Solution Approach 1:
The patent segments the charge transfer process into distinct phases: charge accumulation in the photodetector well, trigger condition evaluation, and rapid charge transfer to the floating diffusion node. This segmentation allows the system to maintain high spatial resolution through precise pixel structure while reducing overall transfer time by only activating the transfer mechanism when needed.
Solution Approach 2:
The patent changes the operational parameters of the photodetector and readout circuitry dynamically. The photodetector operates in linear mode with adjustable gain, and the readout circuit transitions between high-impedance and low-impedance states, enabling fast charge transfer when triggered while maintaining manufacturing robustness through standard CMOS processes.
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 by enhancing sensitivity and resolution, reducing readout latency by two orders of magnitude, and enabling photon-counting sensitivity, thus addressing the limitations of conventional avalanche-gain sensors.
Implementation Method 1
the light sensor must be able to sense reflected light and register its magnitude and/or time of arrival
Data Source
Figure 1~4
Figure 5~11
AI summary
A sensing device (100) includes a light source (101) to emit light, a light sensor (105) 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 (115) having a photocharge storage capacity in excess of one electron and an output circuit (117) that generates an output signal responsive to light detection within the photodetector with sub-hundred nanosecond latency. A distance determination circuitry (119) 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.