Solid-State Imaging Device Dynamic Range Expansion
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Solution Overview
Problem
Conventional solid-state imaging devices face challenges in expanding dynamic range without increasing chip size, experiencing leakage current issues that lead to afterimages and reduced sensitivity, and require multiple capacitors that limit aperture area and dynamic range expansion.
Innovation Solution
A solid-state imaging device with a photoelectric conversion unit, transfer units, and accumulation units that allow continuous charge transfer and addition within the pixel circuit, using MOS transistors to minimize leakage current and achieve global shutter operation, and a differential circuit with capacitors to enhance signal output and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple capacitors are used to expand dynamic range, then dynamic range is improved, but chip size increases and aperture area is reduced
Solution Approach 1:
The patent combines multiple accumulation functions into a single capacitor by sequentially transferring charges from the photodiode to the same accumulation capacitor at different timing. This merging approach eliminates the need for multiple separate capacitors, thereby expanding dynamic range while minimizing chip size and maximizing aperture area.
Solution Approach 2:
The patent introduces temporal dynamics to the charge accumulation process by enabling the same capacitor to serve multiple accumulation purposes at different time instances. Through controlled transfer timing, the capacitor dynamically accumulates charges from different exposure periods, achieving extended dynamic range without increasing physical capacitor count.
2Productivity
If conventional transfer methods are used, then charge transfer is achieved, but leakage current causes afterimages and reduced sensitivity
Solution Approach 1:
The patent applies preliminary reset actions to the accumulation capacitor before each charge transfer operation. By clearing residual charges beforehand and using controlled transfer timing, the system prevents leakage-induced afterimages while maintaining high charge transfer efficiency and sensitivity.
Solution Approach 2:
The patent ensures continuous controlled transfer of charges from the photodiode to the accumulation capacitor through precisely timed transfer operations. This continuous useful action minimizes idle periods where leakage current could accumulate, thereby reducing afterimages and maintaining high sensitivity throughout the imaging cycle.
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
The solution enables expanded dynamic range without external signal addition circuits, reduces chip size, and improves sensitivity and resolution by effectively transferring and accumulating charges across different accumulation times, achieving a dynamic range comparable to human vision.
Implementation Method 1
a photodiode PD which generates a charge in accordance with incident light
Data Source
AI summary
A solid-state imaging device that is configurable into a small size appropriate for expanding dynamic range includes: a photodiode which is a photoelectric conversion unit that generates charge by incident light; a MOS transistor which is connected to the photodiode and transfers the charge; a floating diffusion region which is a first accumulation unit which accumulates the charge via the MOS transistor; a MOS transistor which is a second transfer unit connected to the floating diffusion region and connected in series to the MOS transistor; and a MOS transistor which is an output unit which outputs, via the MOS transistor, a signal voltage in accordance with an amount of the charge.