Phase Difference Detection Pixel Circuit for Autofocus Speed
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Solid-state imaging devices face challenges in improving autofocusing (AF) speed and accuracy, particularly due to limitations in phase difference detection pixels where sharing amplification transistors and photoelectric conversion units hinder simultaneous exposure and reading, affecting tracking of fast-moving subjects and reducing sensitivity.
Innovation Solution
The implementation of a solid-state imaging device with a pixel array unit where phase difference detection pixels share floating diffusions and amplification transistors with adjacent imaging pixels, allowing simultaneous exposure and reading of multiple photoelectric conversion units without a charge storage unit, thereby enhancing AF speed and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If two photoelectric conversion units share one amplification transistor, then device complexity is reduced, but it becomes impossible to expose and read from both units simultaneously, reducing AF tracking capability for fast-moving subjects
Solution Approach 1:
The pixel array is divided into multiple pixel circuits, with each pixel circuit containing a dedicated amplification transistor for its photoelectric conversion unit. This segmentation allows independent operation and simultaneous reading from multiple photoelectric conversion units without sharing transistors, thereby enabling fast AF tracking while maintaining manageable device complexity through modular circuit design
Solution Approach 2:
The pixel array structure is designed to dynamically switch between different operational modes. Each pixel circuit can independently control its amplification transistor to enable or disable signal amplification based on reading requirements. This dynamic control allows the system to achieve simultaneous exposure and reading from multiple units by coordinating the switching states of individual pixel circuits
2Productivity
If a charge storage unit is provided for each photoelectric conversion unit, then simultaneous exposure and reading is enabled, but the area of the photoelectric conversion unit decreases, reducing sensitivity and AF accuracy
Solution Approach 1:
A transfer transistor is introduced as an intermediary component between the photoelectric conversion unit and the amplification transistor. This transfer transistor enables charge transfer from the photoelectric conversion unit to the amplification transistor without requiring a charge storage unit within the photoelectric conversion unit itself. The transfer transistor acts as a mediator that facilitates simultaneous exposure and reading while preserving the full area of the photoelectric conversion unit for light collection
Solution Approach 2:
The charge transfer path is extended into the temporal dimension by using the transfer transistor to move charges between different time periods. Instead of requiring spatial expansion through charge storage units, the system uses temporal sequencing enabled by the transfer transistor to achieve simultaneous reading from multiple units while maintaining compact photoelectric conversion unit areas
3Device complexity
If the photoelectric conversion unit area is reduced, then device complexity is reduced, but sensitivity and AF accuracy are reduced
Solution Approach 1:
The charge storage function is extracted from the photoelectric conversion unit and relocated to a separate transfer transistor that operates independently. This extraction allows the photoelectric conversion unit to maintain its full area for optimal light collection and sensitivity, while the transfer transistor handles the charge transfer and storage functions externally, separating these functions to optimize both accuracy and complexity
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 improves AF speed and accuracy by enabling simultaneous exposure and reading of multiple photoelectric conversion units, addressing the limitations of existing technologies while maintaining sensitivity and reducing the area required for phase difference detection pixels.
Implementation Method 1
each of the plurality of phase difference detection pixels including a plurality of photoelectric conversion units
Implementation Method 2
a plurality of floating diffusions configured to convert charges stored in the plurality of photoelectric conversion units into voltage
Implementation Method 3
a plurality of amplification transistors configured to amplify the converted voltage in the plurality of floating diffusions
Data Source
AI summary
A solid-state imaging device includes a pixel array unit in which a plurality of imaging pixels configured to generate an image, and a plurality of phase difference detection pixels configured to perform phase difference detection are arranged, each of the plurality of phase difference detection pixels including a plurality of photoelectric conversion units, a plurality of floating diffusions configured to convert charges stored in the plurality of photoelectric conversion units into voltage, and a plurality of amplification transistors configured to amplify the converted voltage in the plurality of floating diffusions.