Multicolor CMOS Pixel Sensor Reset Noise Cancellation
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Solution Overview
Problem
CMOS pixel sensors face challenges in reducing reset noise, particularly in multicolor sensors where variations in reset levels across different color channels can lead to inaccuracies in image capture.
Innovation Solution
The implementation of a high-gain multicolor CMOS pixel sensor design that includes specific transistor and capacitor configurations for each color channel, allowing for reset noise cancellation through feedback mechanisms and dark signal subtraction, enabling simultaneous or individual reading of blue, red, and green signals while managing capacitance to prevent overwhelming of sense nodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If reset noise cancellation mechanisms are implemented in multicolor pixel sensors, then image accuracy is improved, but device complexity increases due to additional transistors and capacitors per color channel
Solution Approach 1:
The pixel sensor is segmented into separate color channels (red, green, blue) with dedicated reset transistors and feedback capacitors for each channel. This segmentation allows independent reset noise cancellation for each color channel, improving overall image accuracy while managing complexity through modular organization
Solution Approach 2:
Feedback capacitors are connected between the sense node and the amplifier input for each color channel, creating a feedback mechanism that cancels reset noise. The feedback capacitor stores the reset level information and subtracts it from the signal, effectively eliminating reset noise while maintaining circuit functionality
2Adaptability or versatility
If multiple photodiodes are positioned at different depths to capture multiple colors, then multicolor detection capability is improved, but manufacturing precision requirements increase due to deep contact structures
Solution Approach 1:
The patent transitions from horizontal arrangement of color filters to vertical stacking of photodiodes at different depths in the silicon substrate. This dimensional change exploits the depth dimension to separate color detection, allowing blue, green, and red photodiodes to be positioned at different depths without requiring complex lateral alignment of contact structures
Solution Approach 2:
Multiple photodiodes are nested vertically within the silicon substrate at different depths, with each photodiode optimized for a specific color wavelength. The nested vertical structure allows compact integration of multiple color channels while reducing the lateral footprint and simplifying contact structure requirements
3Measurement precision
If high-gain amplification is used to improve signal detection, then sensitivity is improved, but reset noise becomes more prominent without cancellation mechanisms
Solution Approach 1:
The reset transistor performs preliminary action by resetting the sense node to a known reference level before signal integration begins. This preliminary reset action establishes a baseline that can be subtracted later, preventing reset noise from contaminating the signal during high-gain amplification
Solution Approach 2:
The feedback capacitor captures the reset level information and feeds it back to the amplifier input, where it is subtracted from the amplified signal. This feedback mechanism ensures that reset noise is cancelled even when high-gain amplification is applied to the signal
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 design effectively cancels reset noise across color channels, improving image accuracy by allowing for precise integration and subtraction of dark signals, thereby enhancing the overall performance of multicolor CMOS pixel sensors.
Implementation Method 1
A red photodiode, a green photodiode and a plurality of blue photodiodes are provided. Each of the blue photodiodes coupled to a blue sense node
Data Source
AI summary
An active CMOS pixel sensor includes a red photodiode and a green photodiode coupled to sense nodes. Blue photodiodes are coupled to a blue sense node through select transistors. A blue reset transistor is coupled between a supply node and the blue sense node. A source-follower transistor is coupled to the blue sense node. A blue row-select transistor is coupled to the source-follower transistor and a biased blue column line. Red and green amplifier transistors have gates coupled to sense nodes, drains coupled to a supply node, and sources. Red and green reset transistors have drains coupled to the drains of the amplifier transistors, sources coupled to the sense nodes. Feedback capacitors couple the sense nodes to the reset transistor drains. Red and green row-select transistors have drains coupled to the sources of the amplifier transistors, sources coupled to biased column lines, and gates coupled to a red-green row-select line.