Photodetection Circuit Mode Switching for Wide Dynamic Range
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Solution Overview
Problem
Current digital sensors, such as avalanche photodiodes, struggle to dynamically adjust their operation mode to match the wide dynamic range of human vision, limiting their ability to effectively sense a broad range of lighting conditions.
Innovation Solution
A photodetection circuit capable of operating in either Geiger mode or linear mode, featuring a tiered structure with avalanche photodiodes for light sensing and signal processing circuits, utilizing 3D CMOS integration and through-silicon vias to maximize pixel fill factor and adapt to varying light conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If avalanche photodiodes are used to approach the dynamic range of the human eye, then sensitivity to single photons is improved, but the ability to dynamically adjust operation mode across wide dynamic range of light conditions deteriorates
Solution Approach 1:
The patent implements dynamic mode switching between Geiger and linear modes by controlling the bias voltage applied to the avalanche photodiode. A mode switching circuit dynamically adjusts the operating mode based on detected light conditions, allowing the sensor to adapt its sensitivity characteristics in real-time to match the dynamic range adjustment capability of the human eye.
Solution Approach 2:
The patent changes the operating parameters of the avalanche photodiode by switching between Geiger mode (high bias voltage above breakdown voltage for single photon detection) and linear mode (lower bias voltage for proportional response). This parameter change enables the sensor to cover a wide dynamic range from single photon sensitivity to bright sunlight conditions.
2Adaptability or versatility
If photodetection circuit is designed with both sensing and processing functions, then dynamic range adjustment capability is improved, but pixel fill factor deteriorates due to area occupied by processing circuits
Solution Approach 1:
The patent transitions from a planar 2D layout to a 3D vertical architecture by stacking the processing tier beneath the sensing tier. This dimensional change allows both photodetection and signal processing functions to coexist within the same pixel area, maximizing the fill factor while maintaining dynamic range adjustment capability through mode switching circuits located in the underlying processing tier.
Solution Approach 2:
The patent nests the processing circuits within the pixel structure by placing them in a separate tier directly beneath the avalanche photodiode sensing element. This nested arrangement integrates processing functionality into the pixel without increasing the lateral footprint, thereby preserving maximum fill factor while enabling dynamic mode switching and signal processing.
3Area of moving object
If tiered structure with processing tier underneath sensing tier is implemented, then pixel fill factor is improved, but device complexity increases due to 3D CMOS integration
Solution Approach 1:
The patent utilizes 3D vertical stacking to separate sensing and processing functions into different tiers, with the processing tier positioned beneath the sensing tier. This vertical integration approach increases pixel fill factor by eliminating lateral overlap between sensing and processing elements, while the complexity is managed through systematic 3D CMOS integration techniques.
Solution Approach 2:
The patent segments the photodetection circuit into distinct functional tiers: a sensing tier containing the avalanche photodiode and a processing tier containing the mode switching and signal processing circuits. This segmentation allows independent optimization of each tier while maintaining compact integration through vertical stacking, balancing fill factor improvement with manageable device complexity.
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
The solution enables wide dynamic range sensing, similar to the human eye, by dynamically biasing avalanche photodiodes, increasing pixel fill factor, and enhancing image sensor resolution, allowing for efficient light detection across diverse lighting conditions.
Implementation Method 1
one or more avalanche photodiodes, which may be used for photodetection
Implementation Method 2
rod cells, which are capable of responding to a single photon of light... avalanche photodiodes (APD), which are the solid state equivalent of photoreceptor cells
Data Source
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AI summary
A photodetection circuit includes an avalanche photodiode and a mode switching circuit that may be configured to selectively switch an operating mode of the photodetection circuit between linear mode and Geiger mode. The photodetection circuit may further include a quenching circuit configured to quench and reset the avalanche photodiode in response to an avalanche event when the photodetection circuit is operated in Geiger mode. The photodetection circuit may additionally include an integration circuit configured to integrate photocurrent output by the photodiode and generate integrated charge units when the photodetection circuit is operated in linear mode. The photodetection circuit may also include a counter configured to count pulses output by the avalanche photodiode when the photodetection circuit is operated in Geiger mode and to count integrated charge units generated by the integration circuit when the photodetection circuit is operated in linear mode.