Image Device Charge Transfer Segmentation for Pixel Saturation
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Solution Overview
Problem
Existing image devices with global electronic shutters face challenges in maintaining high saturation charge amounts while minimizing pixel size, leading to potential image quality degradation due to increased pixel size or periods of charge accumulation loss.
Innovation Solution
The image device incorporates a configuration with photoelectric conversion units, holding units, amplification units, and transfer transistors that allow for sequential charge transfers during read-out periods, enabling accumulation and holding of charges across multiple periods, thereby maintaining saturation charge amounts with reduced pixel size and improved image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the saturation charge amount of the photoelectric conversion unit is increased to increase the saturation charge amount of a pixel, then the saturation charge amount of the pixel is improved, but the area of the photoelectric conversion unit increases resulting in an increased pixel size
Solution Approach 1:
The charge accumulation function is segmented between two distinct units: the photoelectric conversion unit (small capacity) and the holding unit (large capacity). The photoelectric conversion unit converts light to charge and transfers it to the holding unit, which then holds the charge until readout. This segmentation allows the pixel to achieve high saturation charge amount through the holding unit without requiring the photoelectric conversion unit to be large.
Solution Approach 2:
The holding unit acts as an intermediary between the photoelectric conversion unit and the readout circuitry. It receives charge from the photoelectric conversion unit, holds it temporarily, and then transfers it to the amplification unit for readout. This intermediary structure enables the system to achieve high charge capacity without increasing the size of the photoelectric conversion unit or the final pixel area.
2Quantity of substance
If charges are held in holding units without accumulating charges in photoelectric conversion units, then the saturation charge amount of a pixel can be increased without increasing the saturation charge amount of the photoelectric conversion unit, but there is a period in which charges generated by photoelectric conversion are unable to be accumulated resulting in image quality degradation
Solution Approach 1:
The system maintains continuous charge accumulation capability through coordinated operation of multiple photoelectric conversion units and holding units. While one photoelectric conversion unit is transferring charge to its holding unit, another photoelectric conversion unit can simultaneously accumulate new charge. This continuous operation ensures that charge accumulation never stops, eliminating periods where generated charges cannot be accumulated and preventing image quality degradation.
Solution Approach 2:
The charge transfer operation occurs periodically between photoelectric conversion units and holding units in a coordinated sequence. Each photoelectric conversion unit transfers charge to its holding unit at specific intervals, allowing other photoelectric conversion units to continue accumulating charge during the transfer periods. This periodic action pattern ensures continuous overall charge accumulation while enabling systematic readout.
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 allows for a global electronic shutter operation with increased saturation charge amounts and reduced noise, optimizing the sizes of photoelectric conversion and holding units while ensuring consistent charge accumulation across pixels, thus enhancing image quality.
Implementation Method 1
a photoelectric conversion unit that accumulates charges generated by photoelectric conversions
Data Source
AI summary
An image device transfers charges of a previous frame from the holding units to the amplification units, during a read-out period of each frame, the read-out period includes a period in which a plurality of overflow transistors are in an on-state and a first period in which a plurality of photoelectric conversion units accumulate charges, and, during a second period following the first period, the plurality of photoelectric conversion units of the plurality of pixels accumulate charges while the plurality of holding units of the plurality of pixels hold the charges accumulated during the first period. During the first and second periods, each of the plurality of pixels performs a plurality of times of charge transfers from the photoelectric conversion unit to the holding unit. The plurality of times of charge transfers including a charge transfer performed at the end of the second period.