Light Sensing Unit With Coupling Elements For Dynamic Range
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Solution Overview
Problem
Current CMOS image sensors face challenges in achieving high dynamic range, high light sensitivity, and high signal-to-noise ratio (SNR) simultaneously due to limitations in carrier transmission efficiency and the need for larger capacitors, which often result in reduced light sensing area and compromised sensitivity.
Innovation Solution
A light sensing unit and circuit that includes a first light sensing element, a floating node, and coupling elements, allowing carriers to be stored in multiple floating nodes, thereby adjusting capacitance values to enhance dynamic range and SNR without increasing layout area and affecting light sensitivity, with control mechanisms to switch between high dynamic range and high sensitivity operation modes based on ambient light conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the floating node capacitor is enlarged to enhance dynamic range, then signal-to-noise ratio is improved, but light sensing area is reduced
Solution Approach 1:
Multiple floating nodes are merged to function as a single storage unit for carriers. The first floating node receives carriers from the light sensing element, and the second floating node receives transferred carriers from the first floating node. This merging approach increases the total capacitance for storing carriers, thereby improving signal-to-noise ratio and dynamic range without requiring a single large capacitor that would occupy excessive light sensing area.
Solution Approach 2:
The carrier storage function is segmented across multiple floating nodes instead of using a single large capacitor. The first floating node and second floating node are separated but work together through controlled carrier transfer. This segmentation allows the system to achieve the equivalent capacitance of a large capacitor while maintaining a distributed architecture that preserves light sensing area.
2Adaptability or versatility
If multiple exposures are performed to enhance dynamic range, then dynamic range is improved, but light sensitivity and signal-to-noise ratio cannot be simultaneously optimized
Solution Approach 1:
The system dynamically adjusts the capacitance of the floating node by controlling the transfer of carriers between the first floating node and the second floating node. Based on ambient light conditions, the circuit can allocate carriers to different floating nodes to optimize performance. In low-light conditions, carriers are retained in the first floating node to maximize sensitivity, while in high-light conditions, carriers are transferred to the second floating node to expand dynamic range, achieving both high dynamic range and high signal-to-noise ratio simultaneously.
3Productivity
If carrier transmission efficiency is increased to improve light sensitivity, then light sensitivity is improved, but dynamic range is limited by the readable signal range of the output circuit
Solution Approach 1:
The system extends the signal storage dimension by introducing a second floating node that receives carriers transferred from the first floating node. This additional dimensional space for carrier storage expands the readable signal range of the output circuit. By controlling the transfer of carriers between floating nodes, the system can accommodate a wider range of signal intensities, thereby expanding dynamic range without compromising carrier transmission efficiency or light sensitivity.
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 the image sensor to achieve high dynamic range, high light sensitivity, and high SNR by effectively storing carriers in multiple floating nodes, allowing for adaptive operation modes that optimize performance across varying light conditions without sacrificing sensitivity or increasing layout area.
Implementation Method 1
a light sensing element in each pixel performs light sensing; the light sensing element then generates carriers corresponding to sensed light intensity
Data Source
AI summary
A light sensing unit for a light sensing circuit of an image sensor includes a first light sensing element, a first floating node and at least one coupling element. The first light sensing element is used for sensing light to obtain a light sensing result and generating a plurality of carriers accordingly. The first floating node is used for receiving and storing the plurality of carriers generated by the first light sensing element. The at least one coupling element is used for coupling the first floating node to at least one second floating node, and transmitting a part of the plurality of carriers stored in the first floating node to the at least one second floating node to be stored in the at least one second floating node.