Non-Avalanche Depth Sensor Readout for Low-Dark-Current 3D Sensing
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Solution Overview
Problem
Conventional 3D imagers and depth sensors employing solid-state light sensors with electron avalanche gain, such as SPADs and SiPMs, suffer from high dark current, single-electron well capacity, low quantum efficiency, low spatial resolution, and impractically long read-out latency, limiting their effectiveness in depth-sensing applications.
Innovation Solution
The development of low-latency, multi-photowell light sensors with pinned photodiodes and JFET-based devices, which enable rapid charge transfer and sub-nanosecond read-out latency, combined with advanced analog front ends (AFEs) and time-to-digital converters (TDCs) for rapid signal digitization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If avalanche-gain photodetectors (SPADs, SiPMs) are used, then single-photon sensitivity is achieved, but high dark current and noise increase
Solution Approach 1:
The patent extracts the avalanche gain function from the photodetector itself and implements it separately in a dedicated gain stage using low-noise transimpedance amplifiers and feedback mechanisms. This separates the photon detection function (performed by low-noise photodetectors) from the signal amplification function, thereby eliminating the dark current penalty associated with avalanche-gain photodetectors while maintaining single-photon sensitivity
Solution Approach 2:
The patent introduces an intermediary low-noise transimpedance amplifier stage between the photodetector and the readout circuitry. This intermediary stage provides the necessary signal gain without the harmful side effects of avalanche multiplication, acting as a mediator that preserves signal integrity while avoiding dark current generation
2Reliability
If pinned photodiode read-out is implemented, then manufacturing yield and quantum efficiency improve, but read-out latency becomes impractically long (hundreds of nanoseconds)
Solution Approach 1:
The patent implements preliminary action by pre-charging the floating diffusion node and pre-positioning the transfer gate in an optimal state before photon arrival. This preliminary preparation enables the photodetector to immediately respond to incoming photons without the hundreds of nanoseconds latency inherent in conventional pinned photodiode readout sequences
Solution Approach 2:
The patent introduces dynamic control of the transfer gate and floating diffusion node, allowing the readout circuit to adapt its timing and voltage levels in real-time based on the photon detection event. This dynamic operation reduces the fixed latency of conventional systems by enabling faster charge transfer and signal readout while maintaining the manufacturing yield benefits of pinned photodiodes
3Speed
If avalanche-gain photodetectors are used, then fast response is achieved, but spatial resolution and manufacturing yield decrease
Solution Approach 1:
The patent segments the photodetector array into independently addressable pixels with dedicated readout circuitry, allowing each pixel to operate optimally without the spatial resolution degradation caused by avalanche-gain photodetectors. This segmentation enables precise spatial encoding of photon arrival positions while maintaining fast response through parallel processing
Solution Approach 2:
The patent replaces the avalanche multiplication mechanism (a form of controlled electrical breakdown) with a linear photodetection and electronic amplification system. This substitution eliminates the spatial resolution loss and manufacturing yield issues associated with avalanche photodetectors while maintaining fast response through optimized electronic readout circuits
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 capabilities by achieving higher sensitivity, finer resolution, and significantly reduced readout latency, overcoming the limitations of conventional avalanche-gain sensors.
Implementation Method 1
solid-state light sensors (photodetectors)
Implementation Method 2
enable rapid charge transfer and sub-nanosecond read-out latency
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.