Imaging Device Global Electronic Shutter Charge Accumulation
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Solution Overview
Problem
Existing imaging devices face challenges in increasing the amount of saturation charge for pixels while performing global electronic shutter operations, which affects image quality and focus detection capabilities.
Innovation Solution
The imaging device incorporates a configuration with photoelectric conversion portions having multiple accumulation regions and light shielding portions to allow for simultaneous charge accumulation and phase difference focus detection, enabling efficient global electronic shutter operations and improved saturation charge management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the photoelectric conversion portion accumulates electric charge for a longer period to increase saturation charge, then the amount of saturation charge increases, but the rolling shutter effect causes image distortion and the global electronic shutter cannot be properly implemented
Solution Approach 1:
The photoelectric conversion portion is divided into multiple accumulation regions that are electrically isolated from each other. Each accumulation region can independently accumulate electric charge, allowing the system to achieve global electronic shutter operation while maintaining adequate saturation charge capacity through the combined capacity of multiple regions.
Solution Approach 2:
The patent introduces a temporal dimension to charge accumulation by implementing a two-period accumulation mechanism. During a first period, charge is accumulated in the photoelectric conversion portion while second transfer switches are turned on in turns. During a second period, the holding unit holds both charge from the first period and charge from the second period, enabling extended effective accumulation without extending the exposure time of a single region.
2Area of stationary object
If the photoelectric conversion portion size is reduced to decrease pixel area, then the device complexity is reduced, but the saturation charge amount decreases
Solution Approach 1:
By dividing the photoelectric conversion portion into multiple smaller accumulation regions, the patent reduces the area required for each individual photoelectric conversion unit while maintaining the total charge accumulation capacity through the combined capacity of all regions. This segmentation allows for more compact pixel design without sacrificing saturation charge amount.
Solution Approach 2:
The holding unit is prepared in advance to receive and hold electric charge from multiple periods. This preliminary preparation of the holding unit allows the photoelectric conversion portion to be smaller, as it only needs to accumulate charge for a portion of the total accumulation time, with the remainder being held in the pre-prepared holding unit.
3Speed
If the first transfer switch is kept on continuously to transfer charge efficiently, then the charge transfer speed increases, but the photoelectric conversion portion cannot accumulate charge during the transfer period
Solution Approach 1:
The first transfer switch operates periodically rather than continuously. It is turned on during the first period to transfer charge, then turned off during the second period to allow continued charge accumulation in the photoelectric conversion portion. This periodic operation ensures that charge transfer does not interrupt the accumulation process, maintaining both transfer speed and total charge quantity.
Solution Approach 2:
The holding unit serves as an intermediary between the photoelectric conversion portion and the amplification unit. It temporarily stores charge during transfer operations, allowing the first transfer switch to operate efficiently without causing loss of accumulated charge. The holding unit mediates the transfer process, ensuring that charge can be moved when needed without interrupting the accumulation function.
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 the amount of saturation charge for pixels, maintains image quality, and supports phase difference autofocus, even with smaller photoelectric conversion portion charges, by optimizing the charge accumulation and holding periods.
Implementation Method 1
a photoelectric conversion portion configured to accumulate an electric charge generated with incident light
Data Source
AI summary
The imaging device performs a global electronic shutter operation in which exposure periods of a plurality of pixels coincide with each other. In a first period during which a photoelectric conversion portion of at least one of the pixels accumulates an electric charge, signals based on electric charges held in holding portions of the plurality of pixels are sequentially output to an output line. During a second period after the output of the signals from the plurality of pixels is finished, the holding unit of each of the plurality of pixels holds an electric charge.