Dual Mode Source Follower for Mixed Lighting Sensitivity
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Solution Overview
Problem
Existing image capture devices are optimized for either bright or low ambient light scenes, leading to conflicting capacitance requirements that result in suboptimal performance in mixed lighting conditions, with high sensitivity devices prone to noise and low sensitivity devices unable to handle varying light intensities effectively.
Innovation Solution
A dual-mode unit cell with high and low sensitivity paths, including transistors and capacitors, that can dynamically switch between modes to accommodate varying light conditions, allowing for efficient charge accumulation and storage without saturating the circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If low capacitance components are used, then sensitivity is improved for low ambient light scenes, but the device cannot store sufficient charge for bright ambient light scenes
Solution Approach 1:
The pixel is divided into two separate charge storage nodes: a first node with low capacitance for high sensitivity in low light conditions, and a second node with high capacitance for charge storage in bright light conditions. This segmentation allows each node to be optimized for its specific function, resolving the contradiction between sensitivity and charge storage capacity.
Solution Approach 2:
The system dynamically switches between two operational modes by controlling switch states. In the first mode, the low capacitance node is active for high sensitivity measurements. In the second mode, the high capacitance node is activated to handle bright light scenes. This dynamic reconfiguration allows the device to adapt to varying light conditions and resolve the fixed capacitance contradiction.
2Quantity of substance
If high capacitance is used to store charge for bright scenes, then charge storage capacity is improved, but noise increases and sensitivity decreases for low light scenes
Solution Approach 1:
By segmenting the charge storage into two nodes with different capacitance values, the system can select the appropriate node based on lighting conditions. The low capacitance node minimizes noise for low light scenes, while the high capacitance node provides sufficient storage for bright scenes without being continuously present to cause noise in sensitive conditions.
Solution Approach 2:
Switches act as intermediaries that control the connection between the photodetector and the two different capacitance nodes. These switches enable the system to selectively route charge to the appropriate node, preventing the high capacitance node from being active during low light conditions and thus avoiding the noise it would introduce.
3Reliability
If a single optimized design is used, then performance is improved for either bright or low light scenes, but the device cannot effectively handle mixed lighting conditions
Solution Approach 1:
The pixel design incorporates two charge storage nodes with different capacitance characteristics, enabling the single device to perform multiple functions: high sensitivity measurement for low light scenes and high capacity charge storage for bright scenes. This multi-functionality allows the device to adapt to various lighting conditions including mixed scenes, resolving the contradiction between performance consistency and adaptability.
Solution Approach 2:
The system uses dynamic switch control to adapt its operational characteristics in real-time based on lighting conditions. By changing the active configuration between the two nodes, the device maintains reliable performance across diverse scenarios from low light to bright light to mixed lighting conditions.
Data Source
AI summary
In certain embodiments, a unit cell is provided. The unit cell may include a high sensitivity path and a low sensitivity path. The high sensitivity path may include a first transistor and a first switch. The first switch may couple an output node to the first transistor. The low sensitivity path may include a capacitor. A second switch may couple the high sensitivity path to the low sensitivity path. A third switch may couple the high sensitivity path and the low sensitivity path to a voltage node.