Pixel Control Unit for Photoelectric Conversion Blooming Reduction
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Solution Overview
Problem
In solid-state imaging devices, setting different exposure times on a pixel block basis and effectively removing noise components from accumulated charge signals pose challenges due to differences in transfer gate states during charge readout and noise readout, leading to image quality deterioration.
Innovation Solution
A photoelectric conversion device with a pixel unit comprising a photoelectric converter, an output unit, and a transfer transistor, where a pixel control unit manages exposure periods and reset states for each pixel block, using select circuits to control exposure times and prevent charge leakage, allowing for appropriate noise removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the transfer transistor is in an on-state during readout of accumulated charge, then charge can be transferred to the output unit, but charge may leak to adjacent pixels causing blooming and image quality deterioration
Solution Approach 1:
The transfer transistor is set to the off-state in advance before reading out accumulated charge, preventing charge leakage to adjacent pixels before the readout operation begins. This preliminary action eliminates the blooming effect while maintaining the ability to transfer charge when needed.
Solution Approach 2:
The transfer transistor dynamically changes its state based on the operational phase: it is in the off-state during charge accumulation and readout phases to prevent blooming, and can be switched to on-state only when charge transfer to the output unit is required. This dynamic state control resolves the contradiction between preventing blooming and enabling charge transfer.
2Measurement precision
If different exposure times are set on a pixel block basis, then high dynamic range imaging is achieved, but the transfer gate state difference between charge readout and noise readout causes noise removal failure
Solution Approach 1:
The transfer transistor is configured with a specific off-state characteristic that applies uniformly across all pixel blocks, ensuring that the state during charge readout matches the state during noise readout. This localized state control at the transistor level ensures consistent noise removal performance across different pixel blocks with different exposure times.
Solution Approach 2:
The transfer transistor's operational parameter (state) is changed to off-state specifically during the readout phase, creating a consistent condition for both charge and noise readout operations. This parameter change ensures that the transfer gate does not interfere with charge accumulation or noise signal integrity, enabling accurate noise removal while maintaining high dynamic range capability.
3Object-affected harmful factors
If the photoelectric converter is held in reset state outside exposure period, then charge leakage is prevented, but readout noise may interfere with signal accuracy
Solution Approach 1:
The photoelectric converter is placed in the reset state in advance before the exposure period begins, ensuring that no residual charge from previous operations leaks into the current exposure. This preliminary resetting action prevents charge leakage while the subsequent readout of noise signal can proceed with the transfer transistor in off-state to maintain signal accuracy.
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 solution enables accurate noise removal and improved image quality by allowing for customizable exposure times on a pixel block basis, reducing blooming and maintaining consistent charge accumulation periods across pixels.
Implementation Method 1
each of the plurality of pixels includes a photoelectric converter that generates charge by photoelectric conversion
Data Source
AI summary
A photoelectric conversion device includes a pixel unit having pixels arranged to form rows and columns, each including a transfer transistor that transfers charge in a photoelectric converter to an output unit, and a pixel control unit that controls the pixels. The pixel control unit is configured to supply a control signal in accordance with an exposure period individually defined for pixel blocks of the pixel unit to pixels of each pixel block and read out, from each pixel, a first signal obtained when the photoelectric converter is in a reset state and a second signal based on charge accumulated in the photoelectric converter during the exposure period. A period excluding both the exposure period and a readout period of the second signal corresponds to a reset period of the photoelectric converter. The transfer transistor is off in a readout period of the first and second signals.