Photoelectric Pixel Bias Switching for Low-Noise Global Shutter
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Solution Overview
Problem
Existing imaging devices suffer from noise due to variations in charge accumulation caused by different bias voltages applied in global shutter functions, leading to image distortion and brightness differences, particularly in environments with changing brightness.
Innovation Solution
The imaging device employs a configuration where a first bias voltage is applied during an exposure period and a second bias voltage during a non-exposure period, with a capacitance ratio (C2 - C1)/C1 ≤ 1, and includes a charge blocking layer with a thickness greater than 25% of the electrode distance, to reduce charge variation and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a global shutter function is implemented using photoelectric conversion element including organic-material thin film, then start and finish of exposure to light are performed at the same timing for all pixels, but noise increases due to variations in charge accumulation caused by different bias voltages
Solution Approach 1:
The patent applies different bias voltages (first bias voltage during exposure, second bias voltage during non-exposure) to control charge accumulation in the photoelectric conversion element. By changing the voltage parameter according to the operational phase, the patent achieves global shutter functionality while managing noise from charge variations
Solution Approach 2:
The patent implements periodic switching between exposure and non-exposure phases with corresponding bias voltage changes. The photoelectric conversion element alternates between accumulating charges during exposure periods and suppressing charge movement during non-exposure periods, creating a rhythmic operational pattern that enables global shutter while controlling noise
2Adaptability or versatility
If different bias voltages are applied during exposure and non-exposure periods, then global shutter function is achieved, but charge accumulation varies leading to image distortion and brightness differences
Solution Approach 1:
The patent changes the bias voltage parameter between exposure and non-exposure periods to achieve global shutter functionality. The first bias voltage facilitates charge accumulation during exposure, while the second bias voltage suppresses charge movement during non-exposure, thereby maintaining charge accumulation consistency across all pixels
Solution Approach 2:
The patent uses the bias voltage as an intermediary control mechanism to mediate between the need for global shutter operation and the need for stable charge accumulation. By introducing this intermediate control parameter, the patent reconciles the conflicting requirements of adaptability and stability
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 achieves reduced noise and consistent exposure timing across all pixels, minimizing image distortion and brightness variations, even in environments with significant brightness changes.
Implementation Method 1
a photoelectric conversion layer that is positioned between the first electrode and the second electrode, includes a donor semiconductor material and an acceptor semiconductor material, and generates electrons and holes
Data Source
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AI summary
An imaging device includes pixels 24. Each of the pixels 24 includes: a lower electrode 2; an upper electrode 5 that is disposed to face the lower electrode 2; and a photoelectric conversion layer 4 that is positioned between the lower electrode 2 and the upper electrode 5, includes a donor semiconductor material and an acceptor semiconductor material, and generates electrons and holes. Between the lower electrode 2 and the upper electrode 5, a first bias voltage is applied in a first period that is an exposure period and a second bias voltage that is different from the first bias voltage is applied in a second period that is a non-exposure period. (C2 - C1)/C1 ≤ 1 is satisfied, where C1 is a capacitance between the lower electrode 2 and the upper electrode 5 when the first bias voltage is applied between the lower electrode 2 and the upper electrode 5, and C2 is the capacitance between the lower electrode 2 and the upper electrode 5 when the second bias voltage is applied between the lower electrode 2 and the upper electrode 5.