Shared-Pixel Image Sensor ADC Routing for Resolution and Sensitivity
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Solution Overview
Problem
As the degree of integration of pixels increases in high-resolution image sensors, the area of photoelectric conversion elements per pixel decreases, leading to reduced sensitivity and saturation signal charge, which affects the readout efficiency of image sensors.
Innovation Solution
The implementation of a pixel array with shared floating diffusion nodes among multiple photoelectric conversion elements, connected to a plurality of column lines and analog-to-digital converters, allows for efficient readout of sensing signals by converting them into pixel values, thereby enhancing readout efficiency and frame rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the degree of integration of pixels is increased for high-resolution implementation, then the resolution is improved, but the area of photoelectric conversion element per pixel decreases leading to reduced sensitivity and saturation signal charge
Solution Approach 1:
Multiple photoelectric conversion elements (e.g., 2x2=4 elements) share a common floating diffusion node for signal readout. This merging approach allows the sensor to maintain high spatial resolution while each shared node accumulates sufficient signal charge from multiple elements, thereby preserving sensitivity despite increased integration density.
Solution Approach 2:
The floating diffusion node serves multiple functions: it acts as the signal accumulation node for multiple photoelectric conversion elements simultaneously, and also functions as the readout node for converting photocharges to voltage signals. This multi-functionality reduces the need for separate dedicated nodes for each element, enabling higher integration while maintaining performance.
2Productivity
If multiple photoelectric conversion elements share the same floating diffusion node, then the readout efficiency is improved, but the complexity of output line connection increases
Solution Approach 1:
The pixel array is divided into multiple blocks, with each block containing photoelectric conversion elements that share a common floating diffusion node. This segmentation allows systematic organization of shared nodes and their connections to column lines, making the output line connection manageable despite the high degree of sharing.
Solution Approach 2:
Photoelectric conversion elements are arranged in a two-dimensional grid pattern, and sharing is organized along specific directions (e.g., horizontal or vertical grouping). This spatial dimensionality approach allows efficient routing of column lines to access shared nodes without excessive crossing or complexity, as connections follow the structured grid layout.
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 increases the readout efficiency of the pixel array, reduces power consumption, and improves the frame rate of the image sensor by minimizing the number of output lines and read operations required, while maintaining image quality in varying light conditions.
Implementation Method 1
The image sensor generates an image of an object by using a photo-sensing element that reacts according to the intensity of light reflected from the object
Data Source
AI summary
An image sensor includes a pixel array including a plurality of shared pixels including a plurality of photoelectric conversion elements arranged in a first direction and a second direction and connected to a same floating diffusion node, and a plurality of column lines connected to the plurality of shared pixels, extending in the second direction, and arranged in parallel. The image sensor further includes an analog-to-digital conversion circuit including a plurality of analog-to-digital converters (ADCs) connected to the plurality of column lines. At least two first shared pixels consecutively arranged in parallel in at least one of the first and second directions and configured to sense an optical signal of a first color among the plurality of shared pixels are connected to different column lines among the plurality of column lines.