Imaging Device Pixel Charge Accumulation for Blackening Suppression
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Solution Overview
Problem
Imaging devices experience blackening or 'black crush' when imaging high-luminance objects due to signal charge saturation, leading to inaccurate pixel signals, especially under continuous exposure or electronic shutter conditions.
Innovation Solution
An imaging device with a pixel configuration that includes a photoelectric converter, charge accumulation region, and sample-and-hold circuits with specific switch characteristics to prevent signal clipping, allowing for linear output up to a clipping voltage and suppressing blackening without additional circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If correlated double sampling is used to obtain true pixel signals, then measurement precision is improved, but blackening occurs in high-luminance areas due to reference signal fluctuation and pixel signal saturation
Solution Approach 1:
The pixel unit is divided into separate functional regions: a photoelectric converter for generating signal charge and a charge accumulation region for storing it. This segmentation allows the signal charge to be accumulated before reading, preventing saturation during the reset period and eliminating the reference signal fluctuation that causes blackening, while maintaining measurement precision through subsequent correlated double sampling
Solution Approach 2:
Signal charge is accumulated in the charge accumulation region before the readout process begins. This preliminary accumulation ensures that the pixel signal is ready and stable before correlated double sampling is performed, preventing the signal saturation that occurs when high-luminance objects are imaged during the reset period
2Object-affected harmful factors
If a clip transistor is added to prevent output potential from rising, then blackening is suppressed, but device complexity increases
Solution Approach 1:
The clipping function is extracted from a separate circuit component (clip transistor) and integrated into the pixel unit itself through the charge accumulation region. By accumulating signal charge before readout, the pixel structure inherently limits the output potential range, eliminating the need for additional clipping circuitry and reducing overall device complexity
Solution Approach 2:
The charge accumulation region serves multiple functions: it accumulates signal charge to prevent saturation, inherently limits output potential range (replacing the clip transistor function), and maintains compatibility with correlated double sampling. This multi-functionality eliminates the need for separate clipping circuitry while achieving blackening suppression
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 effectively suppresses blackening in high-luminance areas, ensuring accurate pixel signals and reducing peripheral circuit complexity, while allowing for efficient image capture without special circuits.
Implementation Method 1
a photoelectric converter that generates signal charge by photoelectric conversion
Data Source
AI summary
An imaging device includes: a pixel including a photoelectric converter that generates signal charge by photoelectric conversion, and a charge accumulation region that accumulates the signal charge, the pixel being configured to output a signal corresponding to a voltage of the charge accumulation region; a signal line electrically connected to the pixel, the signal being transmitted through the signal line; a first switch that is electrically connected to the signal line and that has input-output characteristics in which an output is linear with respect to an input up to a clipping voltage and the output is clipped at the clipping voltage with respect to the input exceeding the clipping voltage; and a second switch that is electrically connected to the signal line and that has input-output characteristics in which an output is linear with respect to an input.