Solid-State Image Sensor Transfer Gate Driving for Distortion Reduction
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Solution Overview
Problem
CMOS solid-state image sensors face issues with object distortion during electronic shutter operations due to rolling scanning, and increasing dark current with higher ISO sensitivity, which are not effectively addressed by existing technologies without advanced manufacturing techniques.
Innovation Solution
A solid-state image sensor configuration with a photo-electric converter, a holding unit, and transfer gates that allow for full-screen simultaneous holding and dynamic range increase, where the first transfer gate is driven with three or more different electric potentials to reduce dark current and prevent object distortion without requiring advanced manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If rolling scanning is used in electronic shutter operation, then device complexity is reduced compared to mechanical shutter, but object distortion occurs due to scan time per screen
Solution Approach 1:
The image sensor is divided into multiple pixel units that can be independently controlled. Each pixel unit includes a photodiode, holding unit, and transfer gates, allowing segmented control of charge transfer and exposure timing across different regions of the sensor, enabling distortion correction through differential timing control
Solution Approach 2:
Signal charge is transferred to the holding unit immediately upon generation during exposure, before rolling scanning begins. This preliminary transfer action ensures that all pixels complete their exposure simultaneously and hold their charges ready for readout, eliminating the distortion caused by sequential scanning
2Manufacturing precision
If scan rate is increased to reduce scan time per screen, then object distortion is reduced, but dark current increases with higher ISO sensitivity
Solution Approach 1:
The signal charge is extracted from the photodiode and transferred to a separate holding unit immediately after generation. This extraction separates the charge storage function from the photoelectric conversion function, allowing the photodiode to be quickly reset for the next exposure while the held charge is read out separately, reducing the time photodiodes are active and thus reducing dark current
Solution Approach 2:
The transfer gates are dynamically controlled with multiple electric potentials to optimize charge transfer timing and control the potential well depth in the holding unit. This dynamic control allows optimization of both readout speed and dark current suppression by adjusting potential levels based on exposure conditions
3Quantity of substance
If holding unit surface area is increased to maintain saturation charge amount, then dynamic range increases, but device area increases
Solution Approach 1:
Different regions of the pixel structure are assigned different functions with optimized dimensions. The photodiode area is optimized for light collection, while the holding unit is positioned and sized to receive charge efficiently. The transfer gate structure creates a localized potential well that concentrates charge in a small effective area, maintaining saturation charge amount without proportionally increasing total pixel area
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 enables reduced dark current and object distortion during exposure, maintaining saturation charge amount and improving image quality without the need for advanced manufacturing, while allowing for increased ISO sensitivity and dynamic range.
Implementation Method 1
a photo-electric converter that converts incident light into a signal charge
Data Source
AI summary
An imaging device comprises a solid-state image sensor including a plurality of unit pixels, and a driving unit. Each unit pixel includes a photo-electric converter that converts incident light into a signal charge, a holding unit that temporarily holds the signal charge obtained by the photo-electric converter, a first transfer gate arranged between the photo-electric converter and the holding unit, that transfers the signal charge to the holding unit, a charge-voltage converter that converts the signal charge into a voltage signal, and a second transfer gate arranged between the holding unit and the charge-voltage converter, that transfers the signal charge to the charge-voltage converter, and that is in a non-conductive state in the case where an image capturing operation is performed in the photo-electric converter. The driving unit drives the solid-state image sensor so as to supply three or more mutually different electric potentials to the first transfer gate.