CMOS Image Sensor Column Line Parasitic Capacitance Amplification
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Solution Overview
Problem
Current CMOS image sensors face challenges in achieving a high signal-to-noise ratio due to the small pixel size and inherent noise limitations, which restricts voltage amplification within the pixel, leading to inefficiencies in light sensitivity and increased chip surface requirements.
Innovation Solution
The solution involves utilizing the parasitic capacitance of column lines for amplification, eliminating the need for a separate capacitor between the column line and column amplifier, and employing dual amplification channels with different capacitances to enhance dynamic range and signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a separate capacitor is added between the column line and column amplifier for voltage amplification, then the signal-to-noise ratio is improved, but the chip surface area increases
Solution Approach 1:
The patent merges the function of the separate capacitor into the column line itself by utilizing the column line's inherent parasitic capacitance. The column line is designed with specific dimensions and routing to achieve the required capacitance value (e.g., 1-10 pF), thereby combining the signal transmission function and the amplification capacitor function into a single structure, eliminating the need for additional discrete capacitor components and reducing chip surface area.
Solution Approach 2:
The patent converts the previously harmful parasitic capacitance of the column line into a beneficial feature for voltage amplification. By carefully designing the column line's physical characteristics (length, width, routing) to achieve the desired capacitance value, the parasitic effect becomes the functional amplification capacitor, improving signal-to-noise ratio while avoiding additional component area.
2Measurement precision
If the pixel size is reduced to increase the number of pixels, then the image sensor resolution is improved, but the inherent noise increases and light sensitivity decreases
Solution Approach 1:
The patent implements voltage amplification using the column line capacitance and column amplifier before the signal is further processed. This early amplification stage provides feedback stabilization that boosts the weak signal from small pixels, compensating for the reduced light sensitivity inherent in smaller pixel areas, thereby maintaining signal quality and effective resolution.
3Measurement precision
If amplifiers are integrated into each pixel for voltage amplification, then the signal-to-noise ratio is improved, but the light sensitive surface area is reduced
Solution Approach 1:
The patent segments the amplification function from the pixel level to the column level. Instead of integrating amplifiers into each pixel, the amplification functionality is implemented at the column level using the column line capacitance and column amplifier, thereby preserving the entire pixel area for light-sensitive functions while still achieving the desired signal-to-noise ratio improvement through subsequent voltage amplification.
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 reduces kTC noise and increases the signal-to-noise ratio while minimizing chip surface usage, allowing for improved light sensitivity and dynamic range without the need for additional capacitors, thus optimizing image sensor performance.
Implementation Method 1
the at least one column amplifier cooperates with the column lines such that the amplification of the respective output signal depends on the capacitance of the respective column line
Implementation Method 2
a light sensitive diode 11 which is coupled to a supply voltage VPIX via a switch 13
Data Source
AI summary
The invention relates to an image sensor, in particular to a CMOS sensor, having a plurality of light sensitive pixels arranged in rows and columns for the generation of output signals proportional to the exposure, wherein column lines are associated with the columns to supply the output signals to at least one column amplifier for amplification, wherein the at least one column amplifier cooperates with the column lines such that the amplification of the respective output signal depends on the capacitance of the respective column line.