Image Sensor Pixel Structure for Source Follower Gain
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Solution Overview
Problem
Current image sensing devices face challenges in achieving high gain and transfer rate for pixel signals due to limitations in the design of pixel structures, particularly in the sharing of floating diffusion regions and transistor arrangements.
Innovation Solution
The proposed image sensing device incorporates an 8-shared pixel structure with specific arrangements of floating diffusion regions and transistor arrays, including parallel coupling of source follower and selection transistors, which enhances the channel width and reduces resistance, thereby improving source follower gain and increasing the transfer rate of pixel signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If unit pixels share floating diffusion regions in an 8-shared pixel structure, then device complexity is reduced and area is minimized, but source follower gain and signal transfer rate deteriorate
Solution Approach 1:
The pixel array is divided into multiple unit pixel blocks, each containing a specific number of unit pixels that share floating diffusion regions. This segmentation allows optimization of the sharing structure to improve source follower gain while maintaining area efficiency.
Solution Approach 2:
Different regions of the pixel array implement different sharing configurations. Specifically, unit pixels are arranged to share floating diffusion regions in a pattern that optimizes the source follower transistor characteristics, creating local variations in the sharing structure to enhance signal quality.
2Manufacturing precision
If unit pixels share floating diffusion regions, then manufacturing precision requirements are reduced, but signal transfer rate deteriorates
Solution Approach 1:
The pixel structure incorporates dynamic control mechanisms where transistor gating and floating diffusion region configuration can be adjusted during operation to optimize signal transfer rate while maintaining the shared structure benefits.
Solution Approach 2:
The invention modifies key parameters such as transistor channel dimensions, floating diffusion region sizes, and interconnect geometries in the shared pixel structure to simultaneously achieve ease of manufacturing and high signal transfer rates.
3Area of stationary object
If floating diffusion regions are shared among multiple unit pixels, then area is reduced, but source follower gain and transfer rate deteriorate
Solution Approach 1:
The pixel structure implements a nested arrangement where unit pixels are positioned around shared floating diffusion regions in a compact configuration. This nesting maximizes area utilization while maintaining optimal spacing for source follower transistor operation.
Solution Approach 2:
The invention transitions from planar sharing to a three-dimensional arrangement where floating diffusion regions are positioned at different vertical levels or depths, allowing unit pixels to share regions without compromising horizontal spacing requirements for high gain operation.
Data Source
AI summary
An image sensing device is provided to include a pixel array including unit pixel blocks. Each of the unit pixel blocks includes a first subpixel block including a first floating diffusion (FD) region and unit pixels surrounding the first FD region, a second subpixel block including a second FD region electrically coupled to the first FD region and unit pixels surrounding the second FD region. The image sensing device also includes a first pixel transistor array and a second pixel transistor array that are disposed at opposite sides of the first subpixel block in the first direction. The first and the pixel transistor array include a first drive transistor set and a second drive transistor set, respectively.