Dual Source Follower Image Sensor Noise Reduction
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Solution Overview
Problem
Current image sensor devices in electronic devices, particularly in camera modules, face challenges in achieving high pixel density and adjustable focus while maintaining low noise and improved transconductance, especially in secondary camera modules with fixed focus lens systems.
Innovation Solution
The image sensor device incorporates an array of pixels with specific transistor configurations, including source follower transistors, switches, and row selection transistors, which enhance charge conversion into voltage signals, reduce noise, and improve frame rate and image quality by adding extra capacitance and optimizing transistor states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel density is increased in camera modules, then image quality improves, but noise increases and transconductance decreases
Solution Approach 1:
A second source follower transistor is introduced as an intermediary between the photodiode and the first source follower transistor. This intermediate transistor acts as a buffer that isolates the photodiode from the loading effects of the first source follower, thereby reducing noise and improving transconductance while maintaining high pixel density
Solution Approach 2:
The source follower stage is segmented into two separate transistors (first source follower and second source follower) rather than using a single transistor. This segmentation allows the circuit to achieve both low noise and high transconductance by distributing the functional requirements across multiple components
2Measurement precision
If pixel density is increased in camera modules, then image quality improves, but transconductance decreases
Solution Approach 1:
The second source follower transistor serves as an intermediary that boosts the transconductance of the overall pixel circuit. By placing this intermediate stage between the photodiode and the first source follower, the circuit achieves higher transconductance values necessary for high pixel density applications without sacrificing image quality
3Device complexity
If fixed focus lens system is used in secondary camera module, then device complexity is reduced, but adaptability and image quality deteriorate
Solution Approach 1:
The pixel circuit parameters are optimized to compensate for the fixed focus limitation. By adjusting the transistor sizing, capacitance values, and circuit topology parameters, the system achieves improved image quality and noise performance even without focus adjustability, effectively working around the limitation of the fixed focus lens system
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 enhances the image quality and frame rate of image sensor devices by reducing noise and improving transconductance, effectively addressing the limitations of existing technologies in pixel density and focus adjustability.
Implementation Method 1
Each image sensing pixel may include an image sensing photodiode
Data Source
AI summary
An image sensor device may include an array of image sensing pixels arranged in rows and columns. Each image sensing pixel may include an image sensing photodiode, a first source follower transistor coupled to the image sensing photodiode, and a switch coupled to the image sensing photodiode. Each image sensor device may include a second source follower transistor coupled to the switch, and a row selection transistor coupled to the first and second source follower transistors.