Multilayer Pixel Holding Circuit for Global Shutter Image Sensors
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Solution Overview
Problem
In CMOS type solid state image pickup devices, the increased area of the second semiconductor substrate due to the presence of memory and AD conversion circuits for each pixel, particularly with multiple photoelectric conversion portions, hinders cost efficiency and global shutter functionality.
Innovation Solution
The image pickup device employs a multilayer structure with a first semiconductor substrate for photoelectric conversion and a second substrate for pixel circuits and accumulation circuits, where each pixel has multiple photoelectric conversion portions generating distinct voltage signals, and a holding circuit to manage these signals, reducing the need for extensive AD conversion circuits on the second substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If memory and AD conversion circuits are provided on a second semiconductor substrate for each pixel, then global shutter function is achieved, but the area of the second semiconductor substrate is increased
Solution Approach 1:
The pixel unit is segmented into multiple photoelectric conversion portions (first and second photoelectric conversion portions), each capable of independent charge accumulation. This segmentation allows the holding circuits to process charges from different portions separately, improving charge management efficiency and enabling global shutter function without requiring excessive substrate area.
Solution Approach 2:
The patent utilizes a multilayer substrate structure where the first and second photoelectric conversion portions are arranged in different layers (depth dimensions). This three-dimensional arrangement allows simultaneous charge accumulation from multiple portions without increasing the planar footprint of the substrate, effectively resolving the area contradiction.
2Adaptability or versatility
If multiple photoelectric conversion portions are provided for each pixel, then focus detection signal and imaging signal can be simultaneously obtained, but memory and AD conversion circuits are required for each portion, increasing substrate area
Solution Approach 1:
The holding circuit is designed with multiple holding portions that can universally handle charges from different photoelectric conversion portions. The same holding circuit structure serves both focus detection and imaging functions by processing charges from the first and second photoelectric conversion portions through a unified architecture, reducing the need for separate dedicated circuits for each function.
Solution Approach 2:
The patent merges the charge accumulation and holding functions for both focus detection and imaging into a single integrated holding circuit structure. The first and second holding portions are combined within one holding circuit, allowing simultaneous processing of multiple signal types without requiring separate independent circuits for each, thereby reducing overall substrate area.
3Area of stationary object
If AD conversion circuit area is reduced, then substrate area efficiency improves, but processing capability may be compromised
Solution Approach 1:
The AD conversion process is segmented into multiple stages corresponding to the multiple photoelectric conversion portions. Each holding portion prepares charges for AD conversion in an organized sequence, allowing the AD conversion circuit to process multiple signals efficiently without requiring a large area for simultaneous processing of all signals at once.
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 enhances semiconductor substrate area efficiency, supports global shutter functionality, and reduces the cost per chip by minimizing the area of the second semiconductor substrate while maintaining image quality and frame rate.
Implementation Method 1
a plurality of pixels each provided with a plurality of photoelectric conversion portions and outputting a first voltage signal based on a charge of at least one photoelectric conversion portion
Data Source
AI summary
An image pickup device includes a plurality of pixels each provided with a plurality of photoelectric conversion portions and outputting a first voltage signal based on a charge of at least one photoelectric conversion portion of the plurality of photoelectric conversion portions and a second voltage signal based on a combined charge of charges of the plurality of photoelectric conversion portions, and a plurality of holding circuits provided in a one-to-one relationship with the plurality of pixels, the plurality of holding circuits holding voltage signals based on charges generated by the plurality of photoelectric conversion portions, and each one of the plurality of holding circuits includes a plurality of holding portions including a first holding portion that holds the first voltage signal and a second holding portion that holds the second voltage signal.