Solid-State Imaging Device Dual Source Follower Circuit
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Solution Overview
Problem
Conventional solid-state imaging devices face challenges in high-speed pixel signal reading due to increased resistance and capacitance in the output signal line, leading to delayed feedback and reduced sensitivity.
Innovation Solution
The implementation of a circuit configuration with a first and second source follower circuit connected via an intermediate output node, which reduces the resistance and capacitance of the output signal line, allowing for faster signal convergence and higher sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If multiple pixel cells share a common output circuit and output signal line to reduce chip size and power consumption, then device area and power consumption are reduced, but the output signal line increases in length, resistance, and capacitance, causing delayed feedback and reduced sensitivity
Solution Approach 1:
The patent divides the single output circuit into multiple separate output circuits, with each pixel cell having its own dedicated output circuit. This segmentation prevents the output signal line from becoming excessively long, maintaining low resistance and capacitance values, and ensuring fast feedback and high sensitivity while still achieving compact chip size through optimized layout of the multiple output circuits.
2Use of energy by stationary object
If multiple pixel cells share a common output circuit and output signal line, then power consumption is reduced, but the increased resistance and capacitance of the output signal line cause delayed feedback and reduced sensitivity
Solution Approach 1:
The patent segments the output circuit functionality across multiple pixel cells, with each cell having its own output circuit. This approach increases total power consumption compared to a fully shared circuit, but the increased power enables faster charging of the output signal line, reducing feedback delay and improving sensitivity. The patent optimizes the balance between power consumption and performance by designing compact output circuits that minimize the trade-off.
3Area of stationary object
If the output signal line is made longer to connect multiple pixel cells to a shared output circuit, then chip area is reduced, but the resistance and capacitance of the output signal line increase, causing delayed feedback
Solution Approach 1:
The patent segments the output circuit assignment so that each pixel cell has its own dedicated output circuit rather than sharing a common one. This keeps the output signal lines short and maintains low resistance and capacitance, enabling fast signal feedback. The chip area is still optimized through compact arrangement of the multiple output circuits and their associated pixel cells, achieving both fast feedback speed and area efficiency.
4Speed
If pixel cells have individual output circuits to reduce output signal line resistance and capacitance, then signal feedback speed and sensitivity are improved, but device complexity and chip area increase
Solution Approach 1:
The patent implements segmentation by providing each pixel cell with its own output circuit, which improves signal feedback speed by reducing output signal line resistance and capacitance. The circuit complexity is managed through standardized design of the output circuit blocks and optimized layout that groups related components, reducing the overall complexity despite the increased number of circuits. The segmentation is applied selectively to the output stage while other circuitry remains shared where appropriate.
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 enables faster reading of pixel signals by improving signal convergence and increasing sensitivity, while maintaining lower noise levels.
Implementation Method 1
a light receiving element, which photoelectrically converts incident light, and stores a signal charge
Data Source
AI summary
A solid-state imaging device includes a plurality of pixel cells, each of the pixel cells including a light receiving element, a floating diffusion, a first source follower circuit, and a second source follower circuit. The plurality of pixel cells are connected to an output signal line. The light receiving element photoelectrically converts incident light, and stores a signal charge. The floating diffusion converts the signal charge read out of the light receiving element into a signal voltage. The first source follower circuit is connected to the floating diffusion, and outputs an output voltage corresponding to the signal voltage. The second source follower circuit is connected in series with the first source follower circuit, and outputs a pixel signal corresponding to the output voltage.