Pixel Structure with Direct Charge Transfer for Image Sensors
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Solution Overview
Problem
Solid-state image sensors suffer from performance degradation due to parasitic storage node leakage (PSNL) and parasitic light sensitivity (PLS), necessitating improved performance parameters that are also cost and time efficient.
Innovation Solution
The implementation of a pixel structure with a front end and back end configuration, including a photodiode, transfer and reset transistors, amplifiers, and capacitors, which enables correlated double sampling and pipelined readout, reducing noise and power consumption while improving parasitic storage node leakage and light sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional solid-state image sensors are used, then image capture function is achieved, but performance degradation occurs due to parasitic storage node leakage and parasitic light sensitivity
Solution Approach 1:
The patent extracts and removes the parasitic storage node from the pixel structure by implementing a direct transfer of photocharge from the photodiode to the floating diffusion node, eliminating the source of parasitic storage node leakage and improving reliability
Solution Approach 2:
The patent introduces a transfer transistor as an intermediary device to move photocharge directly from the photodiode to the floating diffusion node, bypassing the need for a parasitic storage node and thereby eliminating leakage issues while maintaining proper charge transfer function
2Reliability
If conventional solid-state image sensors are used, then image capture function is achieved, but performance degradation occurs due to parasitic light sensitivity
Solution Approach 1:
The patent removes the parasitic storage node that causes parasitic light sensitivity by implementing direct charge transfer from photodiode to floating diffusion, thereby eliminating the harmful light sensitivity while preserving the desired imaging function
Solution Approach 2:
The patent converts the potential harm of complex charge storage structures into benefit by using a simplified direct transfer architecture that eliminates parasitic light sensitivity while maintaining efficient photocharge collection and transfer capabilities
3Measurement precision
If complex pixel structures with multiple transistors and capacitors are implemented, then noise reduction and performance improvement are achieved, but device complexity increases
Solution Approach 1:
The patent segments the pixel structure into distinct functional blocks (photodiode, transfer transistor, floating diffusion node, amplifier) with clear interfaces between them, enabling noise reduction through proper signal isolation while maintaining manageable complexity through modular design
Solution Approach 2:
The patent implements correlated double sampling with feedback mechanisms that read and subtract noise components from the signal path, reducing measurement noise while using a relatively simple pixel structure that doesn't require excessive transistors or capacitors
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 low-noise, high-speed imaging with improved shutter efficiency, reduced parasitic storage node leakage, and lower power consumption, effectively addressing the performance degradation issues in existing image sensors.
Implementation Method 1
a photodiode 16
Data Source
AI summary
In accordance with an embodiment, a pixel includes a first stage coupled to a second stage. The second stage includes a sampling capacitor and a subtraction capacitor.