AD Conversion Unit Composite Signal Generation
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Solution Overview
Problem
Photoelectric conversion devices face challenges in improving signal-to-noise ratio (S/N ratio) and dynamic range while maintaining high-speed readout, as existing technologies either degrade image quality due to offset and gain errors or increase readout time, and lack sufficient study on S/N ratio and dynamic range when increasing speed.
Innovation Solution
A photoelectric conversion device with a pixel and an AD conversion unit that performs multiple AD conversions on the same analog signal using different AD conversion periods with varying reference signal rates, allowing for the generation of multiple digital signals that are composited to improve image quality and S/N ratio, while also enabling faster readout.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If multiple amplifiers with different amplification factors are used to expand dynamic range, then dynamic range is improved, but image quality degrades due to offset and gain errors between output signals
Solution Approach 1:
The patent combines multiple AD conversion results obtained at different amplification factors into a single composite signal. The signal processing unit merges the first AD conversion result (short period, high amplification) and second AD conversion result (long period, low amplification) to produce a final output signal, thereby achieving both extended dynamic range and maintained image quality through systematic integration of multiple conversion paths
2Manufacturing precision
If the same signal processing circuit sequentially performs signal processing at different amplification factors, then image quality is maintained, but readout time increases
Solution Approach 1:
The patent employs periodic action by performing multiple AD conversions on the same analog signal with different AD conversion periods. The control unit orchestrates sequential AD conversions where the first conversion uses a shorter period and the second uses a longer period, allowing the system to gather multiple measurement results without requiring sequential processing through different physical circuits, thus maintaining image quality while optimizing readout efficiency
3Productivity
If AD conversion period is shortened to increase readout speed, then readout time is reduced, but S/N ratio and dynamic range are insufficiently studied
Solution Approach 1:
The patent applies partial or excessive action by performing multiple AD conversions with different period lengths on the same analog signal. The first AD conversion uses an excessively short period to maximize speed, while the second uses a longer period to ensure adequate S/N ratio. The signal processing unit then selectively combines these results, using the short-period result when appropriate and the long-period result when higher precision is needed, thereby achieving both high readout speed and reliable S/N ratio
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 approach enhances the S/N ratio and dynamic range of the photoelectric conversion device while maintaining high-speed readout, reducing image quality degradation and readout time, and effectively addressing the limitations of existing technologies.
Implementation Method 1
a pixel including a photoelectric conversion unit
Implementation Method 2
an AD conversion unit that performs an AD conversion on an analog signal generated in the pixel by comparing a level of the analog signal with a level of a reference signal
Data Source
AI summary
The disclosed photoelectric conversion device includes a pixel including a photoelectric conversion unit, an AD conversion unit that performs an AD conversion on an analog signal generated in the pixel, and a control unit configured to control the AD conversion unit. The control unit is configured to control the AD conversion unit to perform a plurality of times of the AD conversion on the same analog signal. A length of a first AD conversion period of the plurality of times is shorter than a length of a second AD conversion period of the plurality of times. A change rate of the reference signal in the second AD conversion period is smaller than a change rate of the reference signal in the first AD conversion period. In each of the first and second AD conversion periods, a potential of the reference signal changes to a first level.