Column Amplifier Switching for Wide-Dynamic-Range Image Sensors
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Solution Overview
Problem
Existing solid-state imaging apparatuses face challenges in enhancing the signal-to-noise (S/N) ratio and dynamic range expansion due to complex circuits and reduced operation speed, as they require multiple memory units and time-lag feedback mechanisms for amplification factor control.
Innovation Solution
The proposed imaging apparatus employs a configuration with column amplifiers applying different amplification factors to pixel signals, A/D converters, and replacing units that select signals based on a threshold, along with a bit conversion unit to enhance the S/N ratio and dynamic range, allowing for sequential selection and processing of signals with varied amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If pixel signal level detection unit and feedback unit are provided for each column to control amplification factors, then dynamic range expansion is achieved, but circuit complexity increases
Solution Approach 1:
The pixel array is divided into multiple columns, with each column having its own amplifier and A/D converter that can independently select between two amplification factors. This segmentation allows parallel processing of signals with different amplification levels across columns, achieving dynamic range expansion without requiring complex centralized control circuits.
Solution Approach 2:
The system dynamically selects between two amplification factors (first and second amplification factors) for each column based on signal level requirements. This dynamic switching capability allows the circuit to adapt to varying signal conditions while maintaining a relatively simple fixed circuit structure, resolving the contradiction between adaptability and complexity.
2Reliability
If amplification factors are controlled based on detection results, then S/N ratio enhancement is achieved, but time lag of one frame occurs
Solution Approach 1:
Two sets of amplification circuits are prepared in advance, each with a different amplification factor. The system performs A/D conversion for both amplification levels simultaneously or in rapid succession within the same frame period, eliminating the need for feedback-based adjustment that would introduce time lag. The appropriate signal is then selected based on preliminary assessment of signal levels.
Solution Approach 2:
The system maintains continuous operation by processing signals with both amplification factors within the same frame period, ensuring that no frame is lost due to feedback delays. This continuous processing approach allows the system to maintain high frame rates while still achieving S/N ratio enhancement through selective use of appropriate amplification levels.
3Adaptability or versatility
If two memory units are provided for storing high intensity correction signals and pixel signals, then dynamic range expansion is achieved, but circuit size increases
Solution Approach 1:
The system merges the functionality of multiple memory units by using a single memory structure to store both high-intensity correction signals and pixel signals. The signals are multiplexed in the time domain, with different amplification factors applied at different times or to different columns, allowing efficient storage without requiring separate dedicated memory units for each signal type.
Solution Approach 2:
Instead of expanding memory capacity in the spatial dimension (adding more memory units), the system utilizes the time dimension by sequentially processing and storing signals with different amplification factors. This temporal multiplexing approach achieves dynamic range expansion while maintaining compact memory architecture, effectively trading time for space.
4Adaptability or versatility
If pixel signals and high intensity correction signals require exposure and read operations for two frames with different accumulation times, then dynamic range expansion is achieved, but operation speed decreases
Solution Approach 1:
The system employs periodic switching between two amplification factors within each frame period, allowing both high-gain and low-gain signals to be acquired systematically. This periodic action enables the system to maintain high frame rates by alternating between different amplification modes rather than requiring separate exposure periods for each amplification level.
Solution Approach 2:
The system performs A/D conversion for both amplification levels in advance within the same frame period, preparing both high-intensity and low-intensity signal data before final processing. This preliminary processing eliminates the need for separate frame exposures, maintaining high operation speed while achieving dynamic range expansion through selective signal combination.
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 enables efficient S/N ratio enhancement and dynamic range expansion without increasing circuit size or causing operation speed decreases, allowing for precise signal processing and reduced noise levels across varying light conditions.
Implementation Method 1
a plurality of pixels, each including a photoelectric conversion element
Data Source
AI summary
An imaging apparatus includes: a plurality of column amplifiers, each outputting, based on the same one pixel, first and second pixel signals derived by amplifying the signal by different amplifying factors p and q; a plurality of column A/D converters for performing analog to digital conversion of the first and second pixel signals obtained; a plurality of replacing units, each selecting the first pixel signal converted by the corresponding column A/D converter when the first pixel signal converted by the corresponding column A/D converter is smaller than a threshold value, and selecting the second pixel signal converted by the corresponding column A/D converter when the first pixel signal converted by the corresponding column A/D converter is equal to or larger than the threshold value; and a horizontal scanning circuit for successively selecting the first or second pixel signals selected by the replacing units.