Image Sensor Signal Generation Reducing Fixed Pattern Noise
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Solution Overview
Problem
Image sensors suffer from fixed pattern noise (FPN) due to variations in analog signals from unit pixels caused by different characteristics, which degrade image quality.
Innovation Solution
An image sensor design that includes a light-electron conversion unit, a signal generation unit, and a selection unit, where the signal generation unit generates first and second analog signals based on photo-charges accumulated in a storage node, and the selection unit generates an image signal by selecting between these signals based on transmission control signals, effectively reducing FPN by varying the strength of signal transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single analog signal is generated from photo-charges in a storage node, then the device structure is simple, but fixed pattern noise reduces image quality
Solution Approach 1:
The patent divides the single analog signal generation process into two separate signal paths: a first analog signal path with a first transmission transistor and a second analog signal path with a second transmission transistor. This segmentation allows independent control and compensation of threshold voltage variations in each transistor, reducing fixed pattern noise while maintaining manageable device complexity through systematic design.
Solution Approach 2:
The patent utilizes parameter changes by applying different gate voltages to the first and second transmission transistors during different time periods. The first transmission transistor operates during a first time period with a first gate voltage, while the second transmission transistor operates during a second time period with a second gate voltage. This temporal and parametric differentiation enables compensation for threshold voltage differences, improving image quality without significantly increasing structural complexity.
2Productivity
If transmission control signals are applied to transfer photo-charges, then signal generation is efficient, but threshold voltage differences cause fixed pattern noise
Solution Approach 1:
The patent implements dynamic operation by enabling the first transmission transistor during a first time period and the second transmission transistor during a second time period, with each transistor being controllable based on temporal dynamics. This dynamic time-division approach allows efficient signal generation while compensating for threshold voltage differences through sequential operation, maintaining both productivity and signal consistency.
Solution Approach 2:
The patent employs periodic action by alternately activating the first and second transmission transistors in different time periods. The first transmission control signal activates the first transistor in a first period, while the second transmission control signal activates the second transistor in a second period. This periodic activation pattern enables efficient photo-charge transfer while reducing fixed pattern noise through temporal separation, balancing signal generation efficiency with signal consistency.
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 effectively reduces fixed pattern noise by generating image signals that minimize variations caused by threshold voltage differences in transmission transistors, thereby improving image quality.
Implementation Method 1
a light-electron conversion unit configured to generate photo-charges from incident light
Data Source
AI summary
An image sensor includes a light-electron conversion unit, a signal generation unit, and a selection unit. The light-electron conversion unit generates photo-charges from incident light. The signal generation unit accumulates photo-charges from the converter in a storage node during a detection period, and then generates a first analog signal and a second analog signal during an output period. The analog signals are generated based on an amount of photo-charges accumulated in the storage node. The selection unit generates an image signal based on one of the first analog signal and the second analog signal.