Pixel Circuit Shared Reset Node Wiring Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
CMOS image sensors face challenges in reducing metal wiring to accommodate increasing pixel density, as smaller pixel sizes require less metal wiring to ensure sufficient space for photodiodes while maintaining optical efficiency and signal quality.
Innovation Solution
The solution involves coupling a reset control signal node of one pixel circuit to another to share reset and power supply voltages, eliminating the need for separate metal wiring to the floating diffusion node and source follower transistor, thereby minimizing metal wiring and enhancing the fill factor of the photodiode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If separate metal wiring is provided for reset voltage and power supply voltage to each pixel circuit, then each pixel circuit can operate independently and reliably, but the metal wiring area increases, reducing the fill factor of the photodiode
Solution Approach 1:
The patent merges the reset voltage line and power supply voltage line by having the reset control signal node of one pixel circuit serve dual purposes: it controls the reset transistor of its own pixel circuit and provides the power supply voltage to the source follower transistor of a neighboring pixel circuit. This consolidation eliminates redundant metal wiring while maintaining circuit reliability through shared voltage nodes.
Solution Approach 2:
The reset control signal node is designed with multi-functionality, serving both as a control signal input for the reset transistor and as a power supply voltage source for the source follower transistor of an adjacent pixel circuit. This universal node performs multiple functions that previously required separate dedicated wiring, thereby reducing overall metal wiring area.
2Productivity
If pixel size is reduced to increase pixel density, then more pixels can be accommodated in the same area, but the available space for photodiodes decreases, requiring reduced metal wiring
Solution Approach 1:
By consolidating the reset voltage and power supply voltage delivery into a shared reset control signal node, the patent reduces the total metal wiring area required in each pixel circuit. This freed-up space can then be allocated to enlarge the photodiode area, thereby maintaining or improving optical efficiency even as pixel density increases.
Solution Approach 2:
The patent utilizes the spatial relationship between adjacent pixel circuits in the two-dimensional pixel array, allowing the reset control signal node of one pixel circuit to serve a neighboring pixel circuit. This cross-pixel sharing approach effectively redistributes wiring resources across the pixel array dimension, reducing per-pixel wiring overhead.
3Area of moving object
If more metal wiring is used to ensure sufficient space for photodiodes, then photodiode size can be maintained, but the wiring complexity and area increase, reducing overall image sensor efficiency
Solution Approach 1:
The patent merges multiple voltage supply functions into a single reset control signal node, eliminating redundant metal wiring paths. This reduction in wiring complexity allows for larger photodiode areas to be accommodated within the same pixel circuit footprint, improving the balance between optical efficiency and circuit functionality.
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 metal wiring, allowing for larger photodiode sizes, improved optical efficiency, and enhanced signal-to-noise ratio, leading to better image quality and display resolution.
Implementation Method 1
The APS array 110 includes photodiodes which convert received light of such colors into electrical signals to generate image signals.
Data Source
AI summary
A pixel circuit of an image sensor includes a floating diffusion node and a reset transistor. The reset transistor is coupled between the floating diffusion node and a reset control signal node of another pixel circuit of the image sensor. A voltage applied on the reset control signal node of the other pixel circuit is a reset voltage transmitted to the floating diffusion node via the reset transistor.