SWIR Depth Imaging With Ge Photodiodes Under Dark Current Noise
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Solution Overview
Problem
Existing SWIR imaging systems face challenges with high dark current (DC) levels, leading to degraded signal-to-noise ratios and increased manufacturing costs, particularly in systems using InGaAs-based photodetectors.
Innovation Solution
Utilizing germanium (Ge) photodiodes integrated into CMOS processes with short capture times and high-power laser pulses, combined with active imaging techniques to mitigate DC effects and improve signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If InGaAs-based photodetectors are used for SWIR imaging, then detection performance is achieved, but manufacturing costs increase and dark current levels degrade signal quality
Solution Approach 1:
The patent replaces expensive InGaAs photodetectors with cheaper germanium photodetectors that can be integrated into CMOS processes. Although germanium has higher dark current, the overall system cost is reduced and the dark current issue is managed through software processing techniques rather than requiring expensive hardware solutions.
Solution Approach 2:
The patent changes the photodetector material parameter from InGaAs to germanium, which has different dark current characteristics. This parameter change enables cost-effective manufacturing while the resulting dark current problem is addressed through image processing algorithms that subtract dark current profiles from the captured images.
2Ease of manufacture
If germanium photodiodes are used with high dark current, then manufacturing cost decreases, but signal quality degrades due to increased dark current noise
Solution Approach 1:
The patent performs preliminary measurement of dark current profiles by capturing images of uniform fields (such as uniform illumination or dark frames) before processing the actual target images. These pre-measured dark current profiles are then subtracted from the target images to compensate for the high dark current noise, thereby restoring signal quality.
Solution Approach 2:
The patent implements a feedback mechanism where dark current profiles are continuously measured and used to correct subsequent images. The system adapts to varying dark current conditions by repeatedly measuring and subtracting dark current profiles, effectively compensating for the inherent high dark current noise in germanium photodetectors.
3Device complexity
If photodetectors with high dark current are used, then device complexity is reduced, but detection accuracy decreases due to dark current interference
Solution Approach 1:
The patent replaces complex hardware solutions (such as cooling systems or sophisticated analog circuitry to reduce dark current) with software-based processing techniques. By using image processing algorithms to subtract dark current profiles, the system achieves high detection accuracy without increasing device complexity, leveraging computational methods instead of hardware complexity reduction.
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 enhances signal-to-noise ratio and reduces manufacturing costs, enabling high-resolution SWIR imaging with improved performance and cost-effectiveness compared to InGaAs technology.
Implementation Method 1
Each PS may include one or more PDs (e.g. if color filter array is implemented, PDs which detect light of different parts of the spectrum may optionally be collectively referred to as single PS)
Implementation Method 2
combined with active imaging techniques to mitigate DC effects and improve signal quality
Data Source
AI summary
Depth sensors comprising a focal plane array with photosites (PSs) directed in different directions, each PS operable to detect light arriving from an instantaneous field of view (IFOV) of the PS, a readout-set of readout circuitries (ROCs), each ROC coupled to readout-group PSs by multiple switches and operable to output an electric signal indicative of an amount of light impinging on the readout-group PSs when the read-out group is connected to the respective ROC via at least one of the switches, a controller operable to change switching states of the switches, such that at different times different ROCs of the readout-set are coupled to the readout-group and are exposed to reflections from different distances, and a processor operable to obtain the electric signals from the readout-set indicative of detected levels of reflected light collected from the IFOVs of the readout-group and to determine depth information for an object.