High-Dynamic-Range Pixel With Storage Capacitor
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Solution Overview
Problem
Conventional image sensor pixels have a limited dynamic range due to the small dimensions of photodiodes, which restricts their ability to store photogenerated charges, and increasing pixel dimensions is not a viable solution.
Innovation Solution
Incorporating a storage capacitor connected to the photodiode and a reset MOS transistor, along with a coupling capacitor between the photodiode and sense node, to enhance the storage capacity of photogenerated charges without increasing pixel dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If photodiode dimensions are decreased to form smaller pixels, then pixel dimensions are reduced, but dynamic range decreases
Solution Approach 1:
The pixel is segmented into two separate charge storage regions: a first storage node connected to the photodiode for storing photogenerated charges, and a second storage node connected to a storage capacitor for storing additional charges. This segmentation allows the pixel to maintain small dimensions while achieving extended dynamic range through distributed charge storage across multiple nodes.
Solution Approach 2:
The patent introduces a temporal dimension to charge storage by implementing dual storage nodes that can be activated at different times during the readout cycle. The first storage node operates during the integration phase, while the second storage node becomes active during overflow conditions, effectively adding a time-based dimension to the storage capacity without increasing physical area.
2Quantity of substance
If photodiode dimensions are increased to increase dynamic range, then storage capacity of photogenerated charges increases, but pixel dimensions increase
Solution Approach 1:
The storage capacitor is designed to serve multiple functions: it acts as a secondary storage node for overflow charges, provides charge redistribution capability during readout, and enables dynamic range extension without requiring additional photodiode area. This multi-functionality allows a single component to address multiple requirements, maintaining compact pixel dimensions while achieving enhanced charge storage capacity.
3Quantity of substance
If dual storage nodes are implemented to extend dynamic range, then storage capacity increases, but device complexity increases
Solution Approach 1:
The patent merges the readout circuitry for both storage nodes into a shared amplifier and control logic structure. The same readout amplifier processes signals from both the first and second storage nodes, and a unified control mechanism manages the transfer and readout operations. This merging approach reduces the overall circuit complexity compared to implementing completely separate readout paths for each storage node.
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 configuration allows for a higher dynamic range in image sensor pixels by effectively increasing the storage capacity of photogenerated charges, enabling the detection of a wider range of light intensities without modifying the photodiode's dimensions.
Implementation Method 1
The light received by the pixel causes the generation of electron-hole pairs in photodiode D, the electrons being stored in the photodiode
Data Source
AI summary
A pixel including a photodiode having a first pole coupled through a transfer MOS transistor to a node for sensing charges of a first type stored in the photodiode, and having a second pole connected to a storage capacitor and to a circuit for reading charges of a second type sent to the storage capacitor.