Pixel Readout Structure for Fixed Pattern Noise Reduction
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Solution Overview
Problem
Existing image sensors suffer from unwanted fixed pattern noise due to consistent variations in readout circuits, which current techniques have not entirely eliminated.
Innovation Solution
The proposed solution involves coupling both reference and image voltage sampling capacitors simultaneously to the floating diffusion of each pixel, allowing for differential readout that cancels out noise caused by parasitic capacitances, thereby reducing or eliminating fixed pattern noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional readout techniques are used, then device complexity is reduced, but fixed pattern noise increases
Solution Approach 1:
The readout process is segmented into separate phases: a reference phase where only the reference capacitor is coupled to the floating diffusion, and an image phase where both reference and image capacitors are coupled. This segmentation allows independent measurement and subtraction of noise components, reducing fixed pattern noise without requiring fundamental changes to the circuit architecture.
Solution Approach 2:
A reference capacitor is introduced as an intermediary element that captures the noise signal from the floating diffusion during a reference phase. This reference capacitor serves as a mediator that stores the noise component for later subtraction from the image signal, enabling noise reduction without directly modifying the image capture process.
2Object-affected harmful factors
If differential readout with simultaneous capacitor coupling is implemented, then fixed pattern noise is reduced, but readout time increases
Solution Approach 1:
The readout process uses periodic action by alternating between a reference phase and an image phase in a systematic sequence. During the reference phase, the reference capacitor is coupled to capture noise; during the image phase, both capacitors are coupled to capture the image signal. This periodic alternation enables noise subtraction while maintaining efficient readout timing.
Solution Approach 2:
The reference phase is performed as a preliminary action before the image phase. By first coupling the reference capacitor to measure and store the noise signal, the system prepares the noise reference data in advance, which is then used to subtract from the subsequent image signal, reducing fixed pattern noise without adding significant time penalty.
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 approach effectively reduces or eliminates fixed pattern noise by accounting for voltage changes during the readout process, resulting in improved image sensor performance.
Implementation Method 1
coupling both reference and image voltage sampling capacitors simultaneously to the floating diffusion of each pixel
Data Source
AI summary
Systems and methods for fixed pattern noise reduction in image sensors is disclosed herein. An example method may include simultaneously providing a pixel reference voltage of a pixel to a reference sampling capacitor and a signal sampling capacitor, decoupling the reference sampling capacitor from the pixel, providing a signal voltage to the signal sampling capacitor, and decoupling the signal sampling capacitor from the pixel.